WDG-SIO
Isolated RS-422/485 Communications and Watchdog Card
FUNCTIONAL
DESCRIPTION
This
multifunction card contains a Watchdog Timer, an RS422/485
Serial Communications port, and an internal Temperature Alarm.
The WDG-SIO is a full-length card that installs in "long"
expansion slots of IBM PC/XT/AT and compatible computers.
The following paragraphs describe functions provided by the
WDG-SIO card.
WATCHDOG
It's
a fact of life that computers can fail. If a computer fails
it can cause catastrophic damage. There are two methods to
reduce risk of computer failure; (a) redundancy and (b) a
watchdog circuit. Neither method offers 100% assurance but
both of these methods reduce risk or consequences of failure.
Redundancy, a duplication of computer circuitry, is very expensive.
On the other hand, Chassis Plans' Watchdog card offers excellent protection
from temporary malfunctions at very low cost.
An
application program must communicate with the watchdog circuit
at prescribed intervals. If this communication ("prompt")
is missed, the Watchdog will initiate a computer reset. This
restarts the computer from the beginning of the program. If
the failure was temporary, proper operation is resumed. If,
however, the failure is persistent, the Watchdog will continuously
reset the computer. The more frequently the computer is prompted
(and shorter Watchdog time selected), the less time a faulty
computer has to cause damage.
The
method used by the WDG-SIO card to determine loss of computer
function is as follows:
- A
counter/timer has a number greater than zero set into
it by your application program.
- This
counter/timer counts down toward zero at a 225 Hz rate.
- As
long as the computer is functioning properly, the number
in the counter/timer is periodically re-entered by your
application program before the counter/timer reaches zero.
- If
this software resetting of the timer/counter fails to
occur, the timer/counter reaches zero and a hardware reset
of the computer is attempted.
Implementation
of this watchdog procedure can be accomplished by your application
program, by AUTOEXEC.BAT, or by other appropriate software.
A
type 8254 counter/timer chip is used in the Watchdog circuit.
The clock source for this chip is 225 HZ derived from a crystal
oscillator on the card and is independent of the computer
clock. The watchdog time-out is software programmable from
5 mSec to 291 seconds.
The
address for the Watchdog circuit is completely independent
of the Serial Communication address. It is jumper selectable
anywhere within the I/O address range 000 to 3FF hex.
The
output of the Watchdog circuit is an open-collector transistor
output rated at up to 100 mA. If Option S01is included, then
a Form C relay output is provided at a terminal board. Terminal
1 connects to the normally-closed contact which is returned
to ground through the relay center arm. Terminal 3 is connected
to the normally-open contact until the relay is activated
by a time-out at which time it is connected to ground by the
relay center arm.
COUNTER/TIMER
The
8254 counter/timer chip contains three 16-bit counters. Counter/timer
2 is used by the Watchdog circuit. If your card has Option
S03 is included, then there is access to counter/timers 0
and 1 via a 9-pin I/O connector at the rear of the computer.
On-board clock frequencies of 1.843 MHz, 230 KHz, 28.8 KHz,
3.6 KHz, and 225 Hz are available by DIP switch selection.
Counter/timer gate inputs and counter/timer outputs are via
pins on the I/O connector.
If
Option S03 is included, outputs of counter/timers 0 and 1
are buffered by drivers capable of 120 mA drive and are available
at pins 1 and 6 respectively of the 9-pin connector. If Option
S04 is included, those outputs are also opto-isolated. If
Option S05 was specified, then relays are installed instead
of opto- isolators. Relay K3 actuates on counter/timer 0 and
K2 operates on counter/timer 1 outputs. When a relay actuates,
the normally-open contacts at I/O connector pins 5 and 4 respectively
are closed to pin 2 of the 9-pin I/O connector.
TEMPERATURE
ALARM
The
WDG-SIO card also contains a temperature alarm circuit that
activates if the internal temperature in the computer becomes
excessive. That alarm can initiate an interrupt so that an
early shutdown may be accomplished.
The
alarm is factory set at 50oC. You can adjust this
if you desire.
SERIAL
INTERFACE
The
Serial Interface function of the WDG-SIO card can be used
for either RS422 serial communications or RS485 communications.
(The RS485 specification allows multiple transmitters and
receivers to communicate over a two-wire "party line" bus.)
Opto-isolators are incorporated on this card to provide common-mode
voltage isolation on the Tx, Rx, RTS, and CTS communications
lines.
Type
16550 UART's are used as the Asynchronous Communication Element
(ACE). Use of the same ACE as used in IBM original equipment
makes the card 100% compatible with existing programs when
the base address is set as either COM-1 or COM-2. However,
use of the Serial Interface is not restricted to COM-1 or
COM-2 only. Different addresses can be selected anywhere within
the I/O address range 100-3FF hex.
An
on-board crystal oscillator permits precise selection of baud
rate from 50 to 9600.
The
output transceiver used, the new generation type 75176, is
capable of driving extremely long communication lines at high
baud rates. It can drive 60 mA on balanced lines and can receive
input signals as low as 200 mV amplitude superimposed on common
mode noise of maximum -7V/+12V. In case of communication conflict,
the transceivers feature thermal shutdown.
The
communication lines are loaded at the receiver and biased
at the transmitter. Also, an on-board DC-DC converter provides
isolated power to the transceiver and opto-isolators are provided
in the serial I/O lines.
Two
LED indicators are provided in the Serial Interface circuit.
These LED's blink to indicate activity on the transmitting
and receiving lines and are useful for problem diagnosis.
In
addition to dual, differential Transmit and Receive lines,
single-ended, buffered RTS and CTS lines are provided on the
I/O connector. The RTS line can be used to control the Transmitter
and Receiver. The CTS line can be used to check for proper
installation of the communication cable. To check for proper
cable connection, introduce +5VDC to the CTS line on the cable
side of the connector. Then read the CTS bit by software.
Signal ground and +5 VDC are available at the I/O connector.
Full
duplex, half duplex, or simplex configuration can be selected
by jumper options.
Specifications
Watchdog
Timer
- Time-out:
Software selectable from 5 mSec to 291 Sec in 5 mSec
increments.
- Output
Pulse Width: 4 msec.
- Clock:
225 Hz, crystal controlled.
- Address:
Continuously mappable within 000 to 3FF hex I/O range.
- Relay
Option: Contacts rated at 250 mA at up to 24VDC.
Temperature
Alarm
- Temperature:
Factory preset at 50 oC Adjustable.
- Interrupts:
Jumper selectable from IRQ2 through IRQ7, IRQ10 through
IRQ12, IRQ14 or IRQ15
- Alternate
Output: Can be read on data bit 0
Counter
Output Option
(Counters 0 and1)
- Standard
Output: Open collector transistor, 100 mA
- Opto-Isolated
Output Option: 2 mA at up to 24VDC
- Relay
Output Option: Contacts rated at 250 mA at up to 24VDC
Communications
Interface
- I/O
Connection: 25-pin male D-sub connector compatible with
RS422 and RS485 specifications
- Input
Isolation: 60 Volts, signal to ground and signal to
signal.
- Character
length: 5, 6, 7, or 8 bits.
- Parity:
Even, odd or none.
- Stop
Interval: 1, 1.5, or 2 bits.
- Serial
Data Rates: 50 to 9600 baud (Faster rates available),
Asynchronous, Type 16550 buffered UART.
- Address:
Continuously mappable within 000 to 3FF (hex) range
of AT I/O bus addresses.
RS422/RS485
Differential Communication Mode
- Multipoint:
Compatible with RS422 and RS485 specifications. Up to
32 drivers and receivers allowed on line. Serial communications
ACE used is type 16550.
- Receiver
Input Sensitivity: +200 mV, differential input.
- Common
Mode Rejection: +12V to -7V
- Transmitter
Output Drive Capability: 60 mA, with thermal shutdown.
Environmental
- Operating
Temperature: 0 to +60 degree C.
- Storage
Temperature: -50 to +120 degree C.
- Humidity:
10% to 90% non condensing.
- Size:
13.3 inches. (330mm)
Power
Requirements
- +5
VDC at 420 mA, 500 mA maximum
Regulatory
Compliance 
Declaration of Conformity, and Test Reports are on file.
Users must use appropriate shielded cables.
mark is valid up to 70V isolation.
| Part
Number |
Price(USD)
|
| WDG-SIO |
225.00
|
| Option S01 |
15.00
|
| Option S02 |
10.00
|
| Option S03 |
15.00
|
| Option S04 |
20.00
|
| Option S05 |
25.00
|
View / Download Manual (in
.PDF format)
