Technologic Systems TS-5400, User Manual

TS-5400 User’s Manual 

Technologic Systems 

10/31/03

9

Note:

 the correct jumper (FD or HD) must be installed. See the Table 2 for details

. 

Fail-safe bias resistors are used to bias the TX+, TX- and RX+, 
RX- lines to the correct state when these lines are not being 
actively driven. This is an important consideration, since in a 
typical RS-485 installation, the drivers are frequently tri-stated. If 
fail-safe bias resistors are not present, the 485 bus may be 
floating and very small amounts of noise can cause spurious 
characters at the receivers. 4.7K

Ω

 resistors are used to pull the 

TX+ and RX+ signals to 5V and also to bias the TX- and RX- 
signals to ground.  Termination resistors may be required for reliable operation when running long 
distances at high baud rates.  Termination resistors should only be installed at each end of an RS-485 
transmission line.  In a multi-drop application where there are several drivers and/or receivers attached, 
only the devices at each end of the transmission line pair should have termination resistors.  

A read at I/O location 75h bit 1 will return a "1" when the RS-485 option is installed. 

5.4  Automatic RS-485 TX Enable 

TS-5400 boards support fully automatic TX enable control.  This simplifies the design of half-duplex 
systems since turning off the transmitter via the RTS signal is typically difficult to implement.  The 
COM1 UART transmit holding register and the transmit shift register both must be polled until empty 
before deasserting RTS when using the RTS mode.  The design gets more difficult when using the TX 
FIFO or when using a multi-tasking OS such as Linux.    

In Automatic mode, Timer2 and a Xilinx PLD keep track of the bits shifting out the COM1 UART.  This 
circuit automatically turns on/off the RS-485 transceiver at the correct times.   This only requires the 
TIMER2 to be initialized once based on baud rate and data format, and bit 7 at I/O location 75 must be 
set.   A utility called AUTO485.exe is included in the AUTOEXEC.bat that simplifies this task. 

5.5  Adding Serial Ports 

If your project requires more than two serial ports, additional ports may be added via the PC/104 
expansion bus. Technologic Systems offers three different daughter boards (TS-SER1, TS-SER2, and 
TS-SER4) that add 1, 2, or 4 extra COM ports respectively.  Typically these would be configured as 
COM3 or COM4 or be assigned other higher COM I/O locations. Because DOS only directly supports 
four serial ports, any additional ports beyond four will require DOS software drivers. 

The TS-5400 PC/104 bus has IRQ 5, 6, 7, 9, 12, or 15 available for additional serial ports.  Typically 
each serial port has a dedicated interrupt, but the TS-SER4 allows all four extra serial ports to share a 
single interrupt.   This is very helpful in systems with a large number of serial ports since there are a 
limited number of IRQ lines available.   

6  Digital I/O 

There are 24 Digital Input/Output (DIO) lines available on the TS-5400.  These are available on 2 
headers labeled DIO and LCD.  In addition to the DIO signals, each header also has 5 Volt power and 
Ground available, while the DIO header has an external reset available on pin 12.  The header labeled 
LCD can be used as 11 DIO lines or as an alphanumeric LCD interface (See Section 7).  16 of the DIO 
lines are arranged as two byte-wide ports that can be programmed as either inputs or outputs in groups 
of 4-bits.  An additional 4 of the DIO lines can also be programmed as either inputs or outputs, while the 
remaining 4 have a fixed configuration of 3 inputs and 1 output.  One of the fixed input lines can be 
programmed to cause an interrupt. 
 

Jumper 

Receiver Source 

FD 

Full-Duplex RS-485 

HD 

Half-Duplex RS-485 

232 

RS-232 

Table 1 - COM1 Receiver Source