WDG-2S
Dual-Port Isolated RS-422/485
Communications and Watchdog Card
FEATURES
- Watchdog
timer to monitor computer systems
- Two
Optically-Isolated RS-422/485 Serial Comunication Ports
- Computer
power supply voltage and temperature monitors
- LED
status monitors on transmit and receive lines for troubleshooting
- Spare
16-bit counter timer
FUNCTIONAL
DESCRIPTION
This
multifunction card contains a watchdog timer, two RS422/485
serial communications ports, and an internal temperature
monitor and computer voltage monitor. This 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.
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.
The
watchdog timer provides means for automatic computer reset
in case of processor failure, faulty programs, electrical
noise, and some component failures. The circuit works as
follows: A countdown timer is periodically loaded by the
application program. The application program must communicate
with the watchdog circuit at prescribed intervals. If this
communication ("prompt") is missed, the Watchdog
counter is not updated, reaches zero, and provides an output
that can be used to reset the computer. 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.
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 ports addresses. It is DIP switch
selectable anywhere within the I/O address range 000 to
3FF hex.
Counter/Timer
A
type 8254 counter/timer chip is used in the Watchdog circuit.
The 8254 counter/timer chip contains three 16-bit counters
and the clock source is a crystal oscillator on the card
that is independent of the computer clock. Counter/Timers
1 and 2 are used by the Watchdog circuit. If timeout periods
of 25 milliseconds or greater are desired, then counter/timer
2 is the only one used and placement of a jumper applies
225 Hz pulses to that counter. If timeout periods of less
than 25 milliseconds are desired, then you can place a jumper
that connects the output of counter/timer 1 to counter/timer
2 and a DIP switch permits selection of crystal-controlled
clock frequencies of 3.6 KHz or greater. The watchdog time-out
is programmable from 5msec to 291 seconds. Counter/timer
0 is available for general purpose use. If not required
for the Watchdog time-out period, counter/timer 1 is also
available.
Status
Register
An
ambient-temperature sensing circuit and a voltage monitor
circuit are included on the card. Outputs of these circuits
as well as watchdog and relay-state functions are provided
by a read-only Status Register. If any of the items monitored
exceeds preset limits, data are loaded into the Status Register
and an Interrupt can be generated.
Temperature
Monitor
The
temperature monitor circuit compares the output of an LM334
temperature sensor with a preset DC voltage level. The output
of the comparator circuit can be read at bit 0 of the Status
Register. A "1" in that bit position indicates
that temperature is 60oC or less and a "0"
at that bit position indicates that the temperature is above
60oC.
There
is hysteresis in the sensor. The trip point from "1"
to "0" is approximately 50°C while the change
from "0" to "1" occurs at about 46°C.
Voltage
Monitor
The
four computer power supplies (+5V, -5V, +12V, and -12V)
are monitored. Three data bits in the Status Register provide
information. If those voltages are within tolerance, the
state of those three data bits so signifies. If one or more
is more than 7% outside of their nominal values, then two
or more of those three bits indicate that condition plus
also indicates whether the out-of-tolerance voltage(s) is
high or low.
Watchdog
Counter/Timer Output State
Two
bits of the Status Register indicate the state of the counter/timer
output and provide a readback of the relays respectively.
This is useful at computer initialization because the watchdog
function can be tested without actually changing the state
of the relays.
Serial
Interfaces
The
Serial Interface functions of the WDG-2S card, COM-A and
COM-B, can be used for either RS422 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 the card to provide isolation from common mode voltage
that is present on the Tx, Rx, RTS, and CTS communications
lines.
Type
16550 buffered UART's are used as the Asynchronous Communication
Element (ACE). Use of the same ACE as used in IBM original
equipment makes the cards 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 software selection
of baud rate from 50 to 56K.
The
output transceiver used, 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 each serial Interface circuit.
These LED's blink when there is 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:
Selectable from 255 Hz, 3.6864 kHz, 28.8 kHz, 230
kHz, and 1843 kHz, crystal controlled.
- Address:
Continuously mappable within 000 to 3FF hex I/O range.
- Relay
Output: Contacts rated at 250 mA at up to 24VDC.
Supply
Monitor
- Computer
Voltages: +5 V, -5V, +12V, and -12V are monitored
Any voltage exceeding 7% beyond nominal value generates
a Status Interrupt Request
- Temperature:
Factory preset at 50°C ±2°C Adjustable.
- Interrupts:
Jumper selectable from IRQ2 through IRQ7, IRQ10 through
IRQ12, IRQ14 or IRQ15
- Alternate
Output: Can be read at BASE ADDRESS + 4.
Communications
Interface
- I/O
Connection: 9-pin male D-sub connectors.
- Serial
Ports: Two shielded male D-sub 9-pin connectors compatible
with RS-422 and RS-485 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 56K (Faster or custom 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. Driver/Receivers
used are type 75ALS180.
- 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-2S |
339.00
|
View / Download Manual (in
.PDF format)
