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TS-ISO485
TS-ISO485.jpg
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Schematic

Contents

1 Introduction

TS-ISO485 is a PC/104 (standard format) peripheral board that provides two PC compatible COM ports capable of running up to 115K baud. The TS-ISO485 is compatible with any Technologic Systems' SBC that has a PC/104 connector built-in.

Each COM port has opto-isolated RS-485/RS-422 drivers capable of running in full or half duplex mode. Full-duplex RS-485 is the same as the RS-422. The mode of operation can be selected through on-board jumpers.

On-board logic automatically controls transmit enable for half duplex operation. If RTS is asserted true, then TX driver is forced always on, enabling the full-duplex RS-485 or RS-422 mode. For half-duplex RS-485 mode, RTS must be always deasserted because the TX driver must be turned off in order to receive.

TS-ISO485 features include:

  • Two RS-485/RS-422 capable serial ports
  • Automatic RS-485 mode
  • Full or Half Duplex modes supported (Jumper Configurable)
  • Standard 16C550 UART with 16 byte FIFO
  • Jumper selectable COM port (8 distinct IO locations)
  • Jumper selectable IRQ (IRQ 4,5,6,7,9 are available)
  • Supports IRQ line sharing
  • Compatible with TS ARM and x86 SBCs
  • Transient suppression circuitry for noise immunity
  • Galvanically isolated serial ports
  • Hardware detection of receive character gap of 3 character times
  • On board LEDs show TX and RX activity for each COM port

2 Hardware Configuration

COMA and COMB terminal strip Pin-Out
COM Pin Full-Duplex Signal Half-Duplex Signal
1 Transmit + Tx/Rx +
2 Transmit - Tx/Rx -
3 GND GND
4 GND GND
5 Receive - N/C
6 Receive + N/C

2.1 Full-Duplex/Half-Duplex Jumper Settings

  • A_HD Jumper installed will set COMA for half-duplex, jumper open is full duplex
  • B_HD jumper installed will set COMB for half-duplex, jumper open is full duplex
Jumper settings for COM/IO selection
COM port selected Jumpers ADD3-1
COMA COMB ADD3 ADD2 ADD1
COM3(3E8) COM4(2E8) OFF OFF OFF
COM4(2E8) COM5(3A8) OFF OFF ON
COM5(3A8) COM6(2A8) OFF ON OFF
COM6(2A8) COM7(3A0) OFF ON ON
COM7(3A0) COM8(2A0) ON OFF OFF
COM9(398) COM10(298) ON OFF ON
COM11(390) COM12(290) ON ON OFF
COM15(368) COM16(268) ON ON ON


Jumper settings for IRQ selection
IRQ selected Jumpers IRQ4-2
COMA COMB IRQ4 IRQ3 IRQ2
None None OFF OFF OFF
Reserved OFF OFF ON
IRQ3 IRQ4 OFF ON OFF
IRQ5 IRQ6 OFF ON ON
IRQ4 IRQ3 ON OFF OFF
IRQ6 IRQ7 ON OFF ON
IRQ7 IRQ9 ON ON OFF
IRQ9 IRQ1 ON ON ON
Note: The share jumper will enable IRQ sharing for COMA and COMB using the IRQ selected for COMA.
Note: If you are using TS-ISO485 with a Technologic Systems' ARM SBC, only IRQ lines 5, 6 and 7 are available, then IRQ sharing is recommended (Shared Jumper ON). With a X86 SBC, all the IRQ lines can be used.

3 Driver Support

The standard serial 16C550 COM port interface appears as a selectable PC-compatible COM port for software compatibility and no special drivers are required. For example, the TSLinux distribution already includes Linux drivers for the 16C550 UART chip by default. One can use any terminal emulator, as minicom, to open and configure the serial port in use by this board with the appropriate /dev entry, enabling communication to the modem device plugged on the socket.

3.1 Testing TS-ISO485 With Linux and ARM

All the Technologic Systems' ARM SBCs include Linux installed by default with built-in support for the standard 16C550 UART, making the TS-ISO485 an out-of-the-box solution. Address decode and IRQ jumpers need to be configured prior to use the system. For IRQ selection, remember that only IRQ 5, 6 and 7 are available on ARM systems. On these boards, the ISA IRQ 5 corresponds to ARM IRQ 22, ISA IRQ 6 is ARM IRQ 33 and ISA IRQ 7 is ARM IRQ 40. For that reason, IRQ sharing is highly recommended on ARM systems (Shared Jumper ON). After jumper configuration and power on, Linux will automatically detect the serial ports and will install the proper device entries at /dev. Use the setserial utility to make sure the TSISO485 serial ports are configured properly, or to change any parameter. That is specially useful for IRQ configuration, for example:

$ setserial -g /dev/cua/2
/dev/cua/2, UART: 16550A, Port: 0x89c003e8, IRQ: 40
$ setserial /dev/cua/2 IRQ 22
$ setserial -g /dev/cua/2
/dev/cua/2, UART: 16550A, Port: 0x89c003e8, IRQ: 22

In addition, the file /proc/tty/driver/serial on the Linux proc filesystem provides information about the serial driver and configuration:

$ more /proc/tty/driver/serial
serinfo:1.0 driver:5.05c revision:2001-07-08
2: uart:16550A port:89C003E8 irq:22 baud:9600 tx:104 rx:32 RTS|DTR
3: uart:16550A port:89C002E8 irq:33 baud:9600 tx:88 rx:0
In order to test communication, use the simple echo and cat commands on the Linux shell
prompt. For example:
$ cat < /dev/cua/2 &
$ echo "testing serial" > /dev/cua/3
testing serial
$

Assuming that COMA and COMB are connected, all the TX and RX LEDs will blink and the sent data will be correctly received. If you are using Full-Duplex, wire-connect terminals 5 and 6 of one COM port to the terminals 2 and 1 of the other COM port, respectively, in order to create a connection between COMA and COMB. For Half-Duplex, connect terminal 1 of one COM port to the terminal 1 of the other COM port. Do the same for the terminal 2.

3.2 Note on Mode Selection

When one of the serial ports is open under Linux, Linux asserts RTS true by default. This disables RS-485 half-duplex operation. When RTS is not asserted, RS-485 works normally, meaning that whenever TX data is being sent, PLD logic turns on the TX enable on the RS- 485 transceiver. To use the board in RS-485 full-duplex mode or RS-422 mode, the user will frequently want the TX enable always on. The TX enable can be forced on by asserting RTS. This will keep the TX driver always on, which is frequently desired when operating in RS-422 mode. However, some RS-422 implementations do not want the TX always enabled. In a few unusual implementations, two twisted pairs are used in a "multi-drop" manner. This means that multiple devices may be driving one of the twisted pairs. In this case, the TX enable signal must be true only when transmitting data (this is the same as RS-485 mode). The TSISO485 supports these various modes through use of the RTS signal as a mode selector. The TS-ISO485 features automatic RS-485 mode. In many implementations of RS-485, the user software must control which mode the transceiver is in (TX enabled or RX enabled). Since the UART has a FIFO and TX shift register, it is very difficult for software to know when it is time to switch from TX enabled, to the RX enabled mode. The TS-ISO485 has logic on board that switches it automatically at exactly the correct time, which is when the last bit of the TX character has been shifted out of the UART shift register.

4 Product Notes

4.1 FCC Advisory

This equipment generates, uses, and can radiate radio frequency energy and if not installed and used properly (that is, in strict accordance with the manufacturer's instructions), may cause interference to radio and television reception. It has been type tested and found to comply with the limits for a Class A digital device in accordance with the specifications in Part 15 of FCC Rules, which are designed to provide reasonable protection against such interference when operated in a commercial environment. Operation of this equipment in a residential area is likely to cause interference, in which case the owner will be required to correct the interference at his own expense.

If this equipment does cause interference, which can be determined by turning the unit on and off, the user is encouraged to try the following measures to correct the interference:

Reorient the receiving antenna. Relocate the unit with respect to the receiver. Plug the unit into a different outlet so that the unit and receiver are on different branch circuits. Ensure that mounting screws and connector attachment screws are tightly secured. Ensure that good quality, shielded, and grounded cables are used for all data communications. If necessary, the user should consult the dealer or an experienced radio/television technician for additional suggestions. The following booklets prepared by the Federal Communications Commission (FCC) may also prove helpful:

How to Identify and Resolve Radio-TV Interference Problems (Stock No. 004-000-000345-4) Interface Handbook (Stock No. 004-000-004505-7) These booklets may be purchased from the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402.

4.2 Limited Warranty

Technologic Systems warrants this product to be free of defects in material and workmanship for a period of one year from date of purchase. During this warranty period Technologic Systems will repair or replace the defective unit in accordance with the following process:

A copy of the original invoice must be included when returning the defective unit to Technologic Systems, Inc. This limited warranty does not cover damages resulting from lightning or other power surges, misuse, abuse, abnormal conditions of operation, or attempts to alter or modify the function of the product.

This warranty is limited to the repair or replacement of the defective unit. In no event shall Technologic Systems be liable or responsible for any loss or damages, including but not limited to any lost profits, incidental or consequential damages, loss of business, or anticipatory profits arising from the use or inability to use this product.

Repairs made after the expiration of the warranty period are subject to a repair charge and the cost of return shipping. Please, contact Technologic Systems to arrange for any repair service and to obtain repair charge information.