ICS Advent WDT-1002, Product Manual

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Chapter 1: Introduction
Manual Number: 00650-009-28 Page 1-3
The Temperature Alarm circuit operates on the principle of a PN junction voltage decrease of 2.3
mV/°C of ambient temperature increase. The voltage across five serially-connected PN junctions is
compared with a preset DC level from a potentiometer. The output of the comparator circuit can be
applied, via jumper, to Interrupt outputs and/or can be read on bit 0 of the Temperature Alarm
register at Watchdog base a 4.
The potentiometer is factory set at 50 °C. If you desire to set the alarm at some other temperature,
subtract the ambient temperature from the desired alarm temperature and multiply the difference by
5 X 2.3 mV. Then measure the voltage between pin 4 (-) and pin 5 (+) of U17 and adjust potentiom-
eter RP1 for that calculated value.
Serial Interface
The Serial Interface function of the WDT1000-P card can be used for either RS422 serial communi-
cations or RS485 communications. (The RS485 specification allows multiple transmitters and re-
ceivers to communicate over a two-wire “party line” bus.) Opto-isolators are incorporated on this
card to provide isolation from any noise that is present on the Tx, Rx, RTS, and CTS communica-
tions lines.
Type NS16450 UART’s are used as the Asynchronous Communication Element (ACE). Use of the
same ACE as 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 000-3FF 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 receive input
signals as low as 200 mV differential superimposed on common mode noise of maximum -7V/+12V.
In case of communication conflict, the transceivers feature thermal shutdown.
For increased noise immunity, 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.
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, int5VDC to the CTS line on the cable side of the connec-
tor. 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.