Reading Control Data - Honeywell UDC2500 Product Manual

Modbus Read, Write and Override Parameters plus Exception Codes
Analog Parameters
• Whenever analog register addresses 0001 through 0074 (those that can be changed
via communications) are changed, a Write cycle occurs after receipt of the message
and the response is returned.
Override Parameters
• Override analog register address 007D (computer setpoint) is not stored in non-
volatile memory. It can be changed as frequently as desired with no effect on non-
volatile memory retentivity, but the controller must remain in the slave mode.
Digital Parameters
• Whenever digital configuration register addresses 0080 through 00FA are updated via
communications, the non-volatile memory is updated as soon as the message is
received.
Communications Transfer Rates
• Reads minimum 20mS and writes minimum 200mS
Supported Function Codes
• IR port 20 and 21
• RS485 and Ethernet ports 1,2,3,4,6,16,17,20,21
Communications Modes of Operation
• When the Shed Timer is enabled and a write or override occurs the controller will
enter Slave Mode. The keypad is locked from the operator. The purpose of this mode
is that if communications is lost and the shed timer times out then the controller will
enter a known state of operation. The configuration of the "Shed Mode and Output"
and Shed Setpoint Recall are used to configure the controller's shed state. While in
Slave Mode pushing the MAN/AUTO key enters Emergency Manual mode. The
local operator then has control of the output. The controller is in Monitor Mode if the
Shed timer is disabled.

10.2 Reading Control Data

Overview
The following control data can be read from this instrument:
• Input 1
• Input 2
• PV, SP, Output
Register Addresses
Use the identifying codes listed in Table 10-1 to read the specific items.
A Write request for these codes will result in an Error message.
190 UDC2500 Universal Digital Controller Product Manual 4/07