Despatch Protocol Plus Modbus Communications User Manual

Page 23

Chromalox Instruments and Controls

A-51643 Rev. 6 10/06/03

$0000

COMMUNICATIONS ACCESS CODE

$0005

KEYPAD LOCKOUT

$0007

ALARM ACKNOWLEDGE

$0008

LEVEL 1 PASSWORD (write not allowed while in setup mode)

$0009

LEVEL 2 PASSWORD (write not allowed while in setup mode)

$0010

MANUAL SETPOINT

$0040

TIMER SETPOINT

$0192

RUN/HOLD/STOP

$0194

SEGMENT ADVANCE

4.5 Monitoring and Acknowledgement of Alarms, Events, and Cycle Complete, Discrete

Inputs, and Discrete Outputs

Two input registers allow monitoring of the alarm ($0094) and event ($0095) functions associated with

relay outputs 1-4. The corresponding input register represents a binary pattern that indicates the state of

each function. Bits 0-3 of the holding register value represent item 1-4 respectively. A bit value of 0

indicates off, while a bit value of 1 indicates on. Example: A read of holding register $0098 returns a

value of $0006. This would indicate that alarms 2 and 3 are active.

The cycle complete status is monitored by reading input register $0096. A value of 0 indicates the cycle

is active, while a value of 1 indicates the cycle is complete.

Reading the discrete input addresses-$0000 - $00003 monitors the hardware states of the external inputs

Event 1-4. For details on the return values see 5.2.2 [02] Read Input Discretes. Since these inputs are

active low switch inputs, a returned value of 1 (or on) means the input is active (electrically pulled low).

Reading the discrete output addresses-$0000 - $00003 monitors the hardware states of relays 1-4. For

details on the return values see 5.2.1 [01] Read Outputs.

The audible annunciator can be monitored via input register $0097. A value of 0 indicates the audible

annunciator is off, while a value of 1 indicates on. Acknowledgement of alarms and cycle complete

audible annunciation is handled through the alarm acknowledge holding register ($0007). Writing any

non-zero value to this register will acknowledge the alarm. This register emulates the pressing of the

Page/Reset key during an audible alarm condition.