Black Box Network Card IC183C User Manual

JUNE 2000  
IC058C  
IC183C  
RS-422/485 Serial Interface Plus, 4-Port  
CUSTOMER Order toll-free in the U.S. 24 hours, 7 A.M. Monday to midnight Friday: 877-877-BBOX  
FREE technical support, 24 hours a day, 7 days a week: Call 724-746-5500 or fax 724-746-0746  
Mail order: Black Box Corporation, 1000 Park Drive, Lawrence, PA 15055-1018  
SUPPORT  
INFORMATION  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Contents  
1. Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7  
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8  
2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8  
2.2 What’s Included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8  
2.3 Factory-Default Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8  
2.4 Technical Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9  
2.4.1 Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9  
2.4.2 Modem Control Signals . . . . . . . . . . . . . . . . . . . . . . . 10  
2.4.3 Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10  
2.4.4 Why Use an ISP? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10  
3. Card Setup. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11  
3.1 Address Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11  
3.2 Jumper Selections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14  
3.3 IRQ Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14  
3.4 Interrupt Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15  
3.5 RS-485 Enable Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16  
3.6 Interface Mode Examples J1D – J4D . . . . . . . . . . . . . . . . . . 18  
3.7 Line Termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20  
3.8 Clock Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21  
4. Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24  
4.1 Software Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24  
4.1.1 Windows 3.1x . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24  
4.1.2 Windows 95/98 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24  
4.1.3 Windows NT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24  
4.2 Hardware Installation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24  
5. Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Appendix A: Connector Pin Assignments . . . . . . . . . . . . . . . . . . . . 27  
Appendix B: Board Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29  
Appendix C: Electrical Interface . . . . . . . . . . . . . . . . . . . . . . . . . . . 30  
Appendix D: Asynchronous Communications . . . . . . . . . . . . . . . . 31  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
1. Specifications  
Communication Chip — IC058C: 16750 UART; IC183C: 16950 UART  
Maximum Distance — 4000 ft. (1219.2 m)  
Operation — 2- or 4-wire  
Protocol — Asynchronous  
Speed — IC058C: Up to 460.8 kbps; IC183C: 460.8 kbps and above  
Connectors — (1) DB37 male, (4) DB9 male on included cable  
CE Approval — The unit is CE approved  
Manufacturing — IPC 610-A Class-III standards are adhered to with an 0.1  
visual A.Q.L. and 100% Functional Testing. This printed circuit board is built  
®
to U.L. 94V0 rating and is 100% electrically tested. This printed circuit board  
is solder mask over bare copper or solder mask over tin nickel.  
MTBF — Greater than 150,000 hours (calculated)  
Temperature Operating: 32 to 122°F (0 to 50°C);  
Storage: -4 to +158°F (-20 to +70°C)  
Humidity — 10 to 90% relative humidity, noncondensing  
Power — From PC bus: 600 ma @ 5 VDC  
Size — Half-card; 4.2”H x 3.9”W 8”D (10.7 x 9.9 x 20.3 cm)  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
2. Introduction  
2.1 Overview  
The RS-422/485 Serial Interface Plus, 4-Port provides the PC with four  
additional RS-422/485 serial ports for terminals, modems, printers, etc. The  
Card is RS-485 compatible without special software or drivers. This ability is  
®
®
especially useful in Windows , Windows NT, and OS/2 environments where  
the lower-level I/O control is abstracted from the application program. This  
ability means that you can effectively use the Card in an RS-485 application  
with existing standard RS-232 software drivers.  
2.2 What’s Included  
The Card is shipped with the following items. If any of these items  
are missing or damaged, contact the supplier.  
• RS-422/485 Serial Interface Plus, 4-Port Card  
• DB37 to four DB9 “Spider Cable”  
®
• (2) serial utility software diskettes: (1) for 32-bit Windows ,  
®
(1) for DOS and Windows 3.1x,  
• This User’s Manual  
2.3 Factory-Default Settings  
The factory-default settings are as follows:  
Table 2-1. Factory Default Settings.  
Port #  
Port 1  
Port 2  
Port 3  
Port 4  
Base Address  
3F8  
IRQ  
4
Electrical Specifications  
RS-422  
2F8  
3
RS-422  
3E8  
4
RS-422  
2E8  
3
RS-422  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
To install the Card using factory-default settings, refer to Chapter 4,  
Installation.  
For your reference, record installed Card settings below:  
Table 2-2. Your Installed Card Settings.  
Port #  
Port 1  
Port 2  
Port 3  
Port 4  
Base Address  
IRQ  
Electrical Specifications  
2.4 Technical Description  
The IC058C Card uses the 16750 UART. This chip features programmable  
baud rate, data format, and interrupt control, and a 16-byte input and output  
FIFO. The IC183C card uses the 16950 UART, which features a 128-byte FIFO  
for even better performance.  
2.4.1 FEATURES  
• Automatic RS-485 driver enable/disable allows card to appear to be  
RS-232, requiring no additional drivers  
PAL” option allows for unique OEM address selection  
• “Shareable” IRQs allow more than one port to share a single IRQ  
• IRQs 2/9-7, 10, 11, 12, 15 supported  
• 16750 buffered UARTs (IC058C) or 16950 UARTs (IC183C)  
• 16 Bit address decode allows for easier integration  
• Speeds up to 460.8 kbps available  
• Multiple clocking modes ensure compatibility with existing software  
products  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
2.4.2 MODEM CONTROL SIGNALS  
Some software packages require the use of modem handshake signals such as  
CTS or DCD. Refer to your application software manual to determine the  
requirements for modem control signals. If no requirements are mentioned,  
a safe configuration is to tie DTR to DSR and DCD, and tie RTS to CTS. This  
configuration will typically satisfy the modem control-signal requirements for  
most communications software.  
2.4.3 INTERRUPTS  
A good analogy of a PC interrupt would be a phone ringing. The phone “bell”  
is a request for us to stop what we are currently doing and take up another  
task (speak to the person on the other end of the line). This is the same  
process the PC uses to alert the CPU that a task must be performed. The CPU,  
upon receiving an interrupt, makes a record of what the processor was doing  
at the time and stores the information in the “stack”; this allows the processor  
to resume its predefined duties after the interrupt is handled, exactly where it  
left off. Every main subsystem in the PC has its own interrupt, frequently  
called an IRQ (short for Interrupt ReQuest).  
2.4.4 WHY USE AN ISP?  
An Interrupt Status Port (ISP) is a read-only, 8-bit register that sets a  
corresponding bit when an interrupt is pending. Port 1 interrupt line  
corresponds with Bit D0 of the status port, Port 2 with D1, etc. The use of this  
port means that the software designer now only has to poll a single port to  
determine if an interrupt is pending.  
The ISP is at Base+7 on each port (Example: Base=280 Hex, Status  
Port=287, 28F...etc.). The RS-422/485 Serial Interface Plus Card will allow any  
one of the available locations to be read to obtain the value in the status port.  
All four status ports on the Card are identical, so any one of the four can be  
read.  
Example: This indicates that Port 2 has an interrupt pending.  
Bit Position:  
Value Read:  
7
0
6
0
5
0
4
0
3
0
2
0
1
1
0
0
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
3. Card Setup  
The RS-422/485 Serial Interface Plus, 4-Port Card has several jumper straps  
which must be set for proper operation.  
3.1 Address Selection  
Each port on the Card occupies eight consecutive I/O locations. A DIP switch  
is used to set the base address for these locations. The Card has a unique  
addressing scheme that allows it to be completely compatible with older four  
port RS-422/485 interface adapters and provide for the ability to select  
address combinations more commonly used.  
The first addressing scheme allows the Card to select the addresses for its  
ports from a table of available address combinations.  
Table 3-1 shows the addressing combinations available. If different address  
combinations are required, please contact Technical Support about a custom  
PAL option.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Table 3-1. Available Address Combinations.  
Switch 6  
On  
Switch 7  
On  
Switch 8 Port 1 Port 2 Port 3 Port 4  
Off  
On  
Off  
On  
Off  
On  
Off  
On  
3F8  
2F8  
3E8  
500  
2F8  
3E8  
2E8  
508  
3E8  
2E8  
280  
2E8  
2E0  
288  
On  
Off  
On  
Off  
Off  
On  
510  
518  
Off  
On  
580  
588  
590  
598  
Off  
Off  
1500  
3220  
1508  
3228  
1510  
4220  
1518  
4228  
Off  
Off  
On  
On  
Addresses set up by switches 1-5  
NOTE  
Each COM: port in the system should have a unique address. Typically COM 1: -  
COM4: addresses are 3F8, 2F8, 3E8, and 2E8 Hex.  
Refer to Chapter 5 for common address contentions.  
The second mode of address selection provides the compatibility mode. In  
this mode, the DIP switch sets the base address and the adapter occupies 32  
consecutive I/O locations. Table 3-2 describes the location of each port and  
its relationship to the other ports.  
NOTE  
For switches 1-5 to become active, switches 6, 7, and 8 must be set in the “On” or  
“Up” position.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Table 3-2. Address Selection Table.  
Address lines  
A9  
A8  
2
A7  
3
A6  
4
A5  
5
Address Selected 1  
280-29F  
2A0-2BF  
380-39F  
1A0-1BF  
2E0-2FF  
Off  
On  
On  
Off  
Off  
On  
Off  
Off  
Off  
Off  
Off  
On  
On  
On  
On  
Off  
On  
Off  
On  
Off  
Off  
Off  
Off  
On  
Off  
Figure 3-1 shows the correlation between the DIP-switch setting and the  
address bits used to determine the base address. In the example below,  
address 2E0 is selected as a base. Address 2E0 in binary is XX 10 111X XXXX  
where X = a non-selectable address bit.  
A9  
A5  
ON  
OFF  
1 2 3 4 5 6 7 8  
Figure 3-1. DIP Switch Setting.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Table 3-3. Port to Connector Table.  
Connector Location Address  
Port #  
Example (Base=2E0)  
2E0-2E7  
1
2
3
4
1
Base+0  
2
3
4
Base+8  
2E8-2EF  
Base+16  
Base+24  
2F0-2F7  
2F8-2FF  
3.2 Jumper Selections  
For ease of configuration, the headers are grouped by port. Port 1 headers  
have a J1” prefix, Port 2 headers have the “J2” prefix, etc. For example, the  
header that controls the Port 1 IRQ selection is J1B, the header that controls  
the Port 2 IRQ selection is J2B. Information for configuring the adapter is  
printed directly on the Card. This is particularly useful in field re-  
configuration.  
3.3 IRQ Selection  
Headers J1B through J4B select the interrupt request for each serial port. If  
COM1: is selected, the corresponding jumper must be on the IRQ4 setting. If  
COM2: is selected, the corresponding jumper must be on IRQ3.  
NOTE  
Most communications software applications default COM3: to IRQ4 and COM4:  
to IRQ3. This requires the sharing of interrupts between COM1: and COM3:,  
and between COM2: and COM4:. While this is the default, it is not always the  
best setting. Check your software configuration instructions to determine the  
most appropriate IRQ selection.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
3 4 5 6 7 9 10 11 12 15  
Figure 3-2. Headers J1B – J4B, IRQ Selection.  
Any two or more ports can share a common IRQ by placing the jumpers on  
the same IRQ setting and setting the appropriate selections at J1A through  
J4A. Consult your particular software for IRQ selection. If no interrupt is  
desired, remove the jumper.  
3.4 Interrupt Modes  
Headers J1A through J4A select the interrupt modes for each port. Each port  
must be set in the correct mode to ensure proper operation.  
“N” indicates the (N)ormal, single-interrupt-per-port mode. “S” indicates  
the (S)hared interrupt mode, which allows more than one port to access a  
single IRQ. ‘M’ indicates the inclusion of a 1-Kohm pull-down resistor  
required on one port when sharing interrupts.  
J1A  
N S M  
Figure 3-3. Header J1A, Normal IRQ Mode.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Set the jumpers to “S” for shared interrupt mode on all blocks sharing an  
IRQ except one. Set that port block for “M.” This provides the pull-down  
resistor circuit that makes sharing IRQs possible. If you are using more than  
one Serial Interface Plus Card or a compatible adapter in a bus you should  
only have one port set to “M.” Figure 3-4 shows two ports sharing a single IRQ.  
J1A  
N S M  
J2A  
N S M  
Figure 3-4. Header J1A & J2A, Shared IRQ Mode.  
Set the jumper to “S” if you are using more than one Card in a bus or to  
completely remove the pull-down resistor for hardware compatibility. Setting  
the adapter in this configuration when it is not accompanied by a pull-down resistor  
will prevent the ports from triggering an interrupt.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
3.5 RS-485 Enable Modes  
RS-485 is ideal for multi-drop or network environments. RS-485 requires a tri-  
state driver (not dual-state) that will allow the electrical presence of the driver  
to be removed from the line. The driver is in a tri-state or high-impedance  
condition when this occurs. Only one driver may be active at a time and the  
other driver(s) must be tri-stated. The output modem control signal Request  
To Send (RTS) is typically used to control the state of the driver. Some  
communication software packages refer to RS-485 as RTS enable or RTS  
block-mode transfer.  
One of the unique features of the Serial Interface Plus Card is the ability to  
be RS-485 compatible without the need for special software or drivers. This  
ability is especially useful in Windows, Windows NT, and OS/2 environments  
where the lower-level I/O control is abstracted from the application program.  
This ability means that you can effectively use the Card in an RS-485  
application with existing standard RS-232 software drivers.  
Headers J1D through J4D are used to control the RS-485 mode functions  
for the driver circuit. The selections are RTS” enable (silk-screen “RT”) or  
“Auto” enable (silk-screen “AE”). The “Auto” enable feature automatically  
enables/disables the RS-485 interface. The “RTS” mode uses the “RTS”  
modem control signal to enable the RS-485 interface and provides backward  
compatibility with existing software products.  
Position 3 (silk-screen “NE”) of J1D through J4D is used to control the RS-  
485 enable/disable functions for the receiver circuit and determine the state  
of the RS-422/485 driver. The RS-485 “Echo” is the result of connecting the  
receiver inputs to the transmitter outputs. Every time a character is  
transmitted, it is also received. This can be beneficial if the software can  
handle echoing using received characters to throttle the transmitter or it can  
confuse the system if the software does not. To select the “No Echo” mode  
select silk-screen position “NE.”  
For RS-422/530/449 compatibility, remove the jumpers at J1D through J4D.  
Examples on the following pages describe all of the valid settings for  
J1D-J4D.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
3.6 Interface Mode Examples J1D – J4D  
Figure 3-5. Headers J1D - J4D, RS-422.  
Figure 3-6. Headers J1D - J4D, RS-485 “Auto” Enabled,  
with “No Echo.”  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Figure 3-7. Headers J1D - J4D, RS-485 “Auto” Enabled, with “Echo.”  
Figure 3-8. Headers J1D - J4D, RS-485  
with “No Echo.”  
RTS” Enabled,  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Figure 3-9. Headers J1D - J4D, RS-485 “RTS” Enabled, with “Echo.”  
3.7 Line Termination  
Typically, each end of the RS-485 bus must have line-terminating resistors  
(RS-422 terminates at the receive end only). A 120-ohm resistor is across each  
RS-530/422/485 input in addition to a 1-Kohm pull-up/pull-down  
combination that bias the receiver inputs. Headers J1E through J4E allow the  
user to customize this interface to their specific requirements. Each jumper  
position corresponds to a specific portion of the interface. If multiple Serial  
Interface Plus adapters are configured in a RS-485 network, only the boards  
on each end should have jumpers T, P, and P ON. Refer to the table on the  
next page for each position’s operation:  
P
P
T
L
L
Figure 3-10. Headers J1E - J4E, Line Termination.  
20  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Table 3-4. Jumper Functions.  
Name  
Function  
P
Adds or removes the 1-Kohm pull-down resistor in the  
RS-422/RS-485 receiver circuit (Receive data only).  
P
Adds or removes the 1-Kohm pull-up resistor in the  
RS-422/RS-485 receiver circuit (Receive data only).  
T
L
L
Adds or removes the 120-ohm termination.  
Connects the TX- to RX- for RS-485 two-wire operation.  
Connects the TX+ to RX+ for RS-485 two-wire operation.  
3.8 Clock Modes  
The Serial Interface Plus Card employs a unique clocking option that allows  
the user to select from divide by 4, divide by 2, and divide by 1 clocking  
modes. These modes are selected at Headers J1C through J4C.  
To select the baud rates commonly associated with COM: ports (2400,  
4800, 9600, 19.2, and so on up to 115.2 kbps ) place the jumper in the “divide  
by 4” mode (silk-screen DIV4).  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Figure 3-11. Clocking Mode “Divide By 4.”  
To double these rates up to a maximum rate for 230.4 kbps, place the jumper  
in the “divide by 2” (silk-screen DIV2) position.  
Figure 3-12. Clocking Mode “Divide By 2.”  
To select the maximum data rate (460.8 kbps) place the jumper in the  
“divide by 1” (silk-screen DIV1) position.  
22  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Figure 3-13. Clocking Mode “Divide By 1.”  
23  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
4. Installation  
IMPORTANT  
You MUST set up the operating system BEFORE you physically install  
the Card.  
4.1 Software Installation  
If you are installing an ISA adapter in DOS, OS/2, or QNX, please refer to the  
appropriate directory on one of the Serial Utilities Disks for instructions.  
4.1.1 WINDOWS 3.1X  
Please refer to the /WINDOWS sub-directory on the Serial Utilities Diskette  
for help files and current information on the installation of the Card in  
thisoperating environment.  
4.1.2 WINDOWS 95/98 USERS  
For the ISA card, run setup on disk two of the Serial Utilities Diskettes before  
installing the card. Make note of the resources that Windows assigns the adapter  
and set the adapter to match those resources. Power down the computer and  
install the adapter as described in Section 4.2. If you wish to change any resources  
assigned to the adapter, refer to the help file installed in the Black Box folder in  
the Start, Programs menu.  
4.1.3 WINDOWS NT  
For the ISA card, run setup on disk two of the Serial Utilities Diskettes before  
installing the card. After installing the software, refer to the help file that  
automatically comes up for installation instructions.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
4.2 Hardware Installation  
The RS-422/485 Serial Interface Plus Card can be installed in any of the PC  
expansion slots. The Card contains several jumper straps for each port that  
you must set for proper operation.  
1. Turn off PC power. Disconnect the power cord.  
2. Remove the PC case cover.  
3. Locate an available slot and remove the blank metal slot cover.  
4. Gently insert the Card into the slot. Make sure that the Card is seated  
properly.  
5. Replace the screw.  
6. Replace the cover.  
7. Connect the power cord.  
Installation is complete.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
5. Troubleshooting  
Two Serial Utility Diskettes are supplied with the adapter and will be used in  
the troubleshooting procedures. By using this diskette and following these  
simple steps, most common problems can be eliminated. If you still cannot  
solve your problem, call Black Box technical support at 724-746-5500.  
1. Identify all I/O adapters currently installed in your system. This includes  
your on-board serial ports, controller cards, sound cards etc. The I/O  
addresses used by these adapters, as well as the IRQ (if any) should be  
identified.  
2. Configure your RS-422/485 Serial Interface Plus Card so that there is no  
conflict with currently installed adapters. No two adapters can occupy the  
same I/O address.  
3. Make sure the adapter is using a unique IRQ. While the adapter does  
allow the sharing of IRQs, many other adapters (such as SCSI adapters  
and on-board serial ports) do not. The IRQ is typically selected via an on-  
board header block. Refer to the section on Card Setup for help in  
choosing an I/O address and IRQ.  
4. Make sure the adapter is securely installed in a motherboard slot.  
5. Use the supplied diskette and User Manual to verify that the adapter is  
configured correctly. The supplied diskette contains a diagnostic program  
“SSD” that will verify if an adapter is configured properly. This diagnostic  
program is written with the user in mind and is easy to use. Refer to the  
“README” file on the supplied diskette for detailed instructions on using  
“SSD.”  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
6. The following are known I/O conflicts:  
• The 278 and 378 settings may conflict with your printer I/O adapter.  
• 3B0 cannot be used if a Monochrome adapter is installed.  
• 3F8-3FF is typically reserved for COM1:  
• 2F8-2FF is typically reserved for COM2:  
• 3E8-3EF is typically reserved for COM3:  
• 2E8-2EF is typically reserved for COM4:  
7. Please refer to your included diskette for any post production manual  
updates and application specific information.  
8. Always use the included diagnostic software when troubleshooting a  
problem. This will eliminate the software issue from the equation.  
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RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Appendix A: Connector Pin Assignments  
Table A-1. DB9 Pin Assignments.  
Signal  
GND  
TX+  
Name  
Pin #  
Mode  
Ground  
5
4
3
6
7
1
2
9
8
Transmit Data Positive  
Transmit Data Negative  
Request to Send Positive  
Request to Send Negative  
Receive Data Positive  
Receive Data Negative  
Clear to Send Positive  
Clear to Send Negative  
Output  
Output  
Output  
Output  
Input  
TX-  
RTS+  
RTS-  
RX+  
RX-  
Input  
CTS+  
CTS-  
Input  
Input  
28  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Table A-2. DB37 Pin Assignments.  
Port #  
GND  
TX-  
1
2
3
4
33  
35  
17  
34  
36  
16  
18  
37  
15  
14  
12  
30  
13  
11  
31  
29  
10  
32  
24  
26  
8
5
3
RTS-  
TX+  
21  
4
25  
27  
7
RX-  
2
CTS-  
RTS+  
RX+  
22  
20  
1
9
28  
6
CTS+  
23  
29  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Appendix B: Board Layout  
DIV1  
DIV2  
DIV4  
DIV1  
DIV2  
DIV4  
DIV1  
DIV2  
DIV4  
DIV1  
DIV2  
DIV4  
C3  
C2  
A9  
A8  
A7  
A6  
A5  
S3  
S2  
S1  
AT  
RT  
NE  
AT  
RT  
NE  
AT  
RT  
NE  
AT  
RT  
NE  
R17  
R16  
R15  
R14  
SD837M-318  
Figure B-1. Board Layout.  
30  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Appendix C: Electrical Interface  
RS-422  
The RS-422 specification defines the electrical characteristics of balanced-  
voltage digital interface circuits. RS-422 is a differential interface that defines  
voltage levels and driver/receiver electrical specifications. On a differential  
interface, logic levels are defined by the difference in voltage between a pair  
of outputs or inputs. In contrast, a single-ended interface, for example RS-  
232, defines the logic levels as the difference in voltage between a single  
signal and a common ground connection. Differential interfaces are typically  
more immune to noise or voltage spikes that may occur on the  
communication lines. Differential interfaces also have greater drive  
capabilities that allow for longer cable lengths. RS-422 is rated up to 10  
Megabits per second and can have cabling 4000 feet (1219 m) long.  
RS-422 also defines driver and receiver electrical characteristics that will allow  
1 driver and up to 32 receivers on the line at once. RS-422 signal levels range  
from 0 to +5 volts. RS-422 does not define a physical connector.  
RS-485  
RS-485 is backward-compatible with RS-422; however, it is optimized for  
partyline or multi-drop applications. The output of the RS-422/485 driver is  
capable of being Active (enabled) or Tri-State (disabled). This capability  
allows multiple ports to be connected in a multi-drop bus and selectively  
polled. RS-485 allows cable lengths up to 4000 feet (1219 m) and data rates  
up to 10 Megabits per second. The signal levels for RS-485 are the same as  
those defined by RS-422. RS-485 has electrical characteristics that allow for 32  
drivers and 32 receivers to be connected to one line. This interface is ideal for  
multi-drop or network environments. RS-485’s tri-state driver (not dual-state)  
will allow the electrical presence of the driver to be removed from the line.  
Only one driver may be active at a time and the other driver(s) must be tri-  
stated. RS-485 can be cabled in two ways, two-wire and four-wire mode. Two-  
wire mode does not allow for full-duplex communication, and requires that  
data be transferred in only one direction at a time. For half-duplex operation,  
the two transmit pins should be connected to the two receive pins (Tx+ to  
Rx+ and Tx- to Rx-). Four-wire mode allows full-duplex data transfers. RS-485  
does not define a connector pin-out or a set of modem control signals. RS-485  
does not define a physical connector.  
31  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
Appendix D: Asynchronous  
Communications  
In serial data communications, individual bits of a character are transmitted  
consecutively to a receiver that assembles the bits back into a character. Data  
rate, error checking, handshaking, and character framing (start/stop bits) are  
pre-defined and must correspond at both the transmitting and receiving ends.  
Asynchronous communications is the standard means of serial data  
®
communication for PC compatibles and PS/2 computers. The original PC  
was equipped with a communication or COM: port that was designed around  
an 8250 Universal Asynchronous Receiver Transmitter (UART). This device  
allows asynchronous serial data to be transferred through a simple and  
straightforward programming interface. Character boundaries for  
asynchronous communications are defined by a starting bit followed by a pre-  
defined number of data bits (5, 6, 7, or 8). The end of the character is  
defined by the transmission of a pre-defined number of stop bits (usual  
1, 1.5 or 2).  
Odd, Even  
or  
Idle state of  
line  
Remain idle or  
next start bit  
Unused  
5 to 8 Data Bits  
1
0
P
BIT  
STOP  
1
1.5  
2
Figure D-1. Asynchronous Communications Bit Diagram.  
32  
 
RS-422/485 SERIAL INTERFACE PLUS, 4-PORT  
An extra bit used for error detection is often appended before the stop bits.  
This special bit is called the parity bit. Parity is a simple method of  
determining if a data bit has been lost or corrupted during transmission.  
There are several methods for implementing a parity check to guard against  
data corruption. Common methods are called (E)ven Parity and (O)dd  
Parity. Sometimes parity is not used to detect errors on the data stream. This  
is refereed to as (N)o parity. Because each bit in asynchronous  
communications is sent consecutively, it is easy to generalize asynchronous  
communications by stating that each character is wrapped (framed) by pre-  
defined bits to mark the beginning and end of the serial transmission of the  
character. The data rate and communication parameters for asynchronous  
communications have to be the same at both the transmitting and receiving  
ends. The communication parameters are baud rate, parity, number of data  
bits per character, and stop bits (for example, 9600,N,8,1).  
33  
 
© Copyright 2000. Black Box Corporation. All rights reserved.  
1000 Park Drive  
Lawrence, PA 15055-1018  
724-746-5500  
Fax 724-746-0746  
 

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