11984 Rev01 Page 14 of 15
3.1 Installation
The RS422 format is a two-wire send and two-wire receive configuration. Each
Supervisor to be connected on the network requires a unique base address. Base
address selection switches are located on the Supervisor circuit board, which is
accessed by removing the bottom cover of the Supervisor. The left address switch
(rotary type) is the most significant hex digit. The right address is the least sig-
nificant hex digit. Valid base addresses are separated as every fourth address.
The first valid base address is 00. The second valid base address, for a second
Supervisor, is 04; and the base addresses continue as 08, 0C, 10, 14... etc.
The supported communication format is ASCII text represented as 10 bits per
character: 8 data bits, no parity, 1 start bit and 1 stop bit. The Supervisor will
communicate at a top speed of 9600 baud. It acts as a slave device on the net-
work, accepting commands from the furnace computer. The Supervisor will ac-
knowledge all commands sent to its address with either a simple acknowledge or
an acknowledgement that contains data.
The serial interface is fully described in the PTI publication titled "SENTRY
Supervisor Operation Manual and Serial Communications Programmer’s Guide."
The serial interface allows the process tool controller to access parameters in the
Supervisor menu. Due to the Supervisor's ability to save configuration by using
the "Save Data" command, many parameters can be initialized manually using the
keypad. By storing many of the parameters that are not required to be changed
during normal tool operation, the serial communication requirements can be
simplified to only a few commands: the "power up clear," the "set point" and the
"read process pressure" commands. (These commands are fully described in the
"SENTRY Supervisor Operation Manual and Serial Communications
Programmer’s Guide.")
The following offers a simple test for the serial interface. It is assumed in this
example that there is one Supervisor with the starting base address of 00.
1. Power on the Supervisor
2. Ensure the "StptMode" (Set point Mode) is set to " Single" (see section 3,
page 10, instructions 1 and 2).
3. The first command that the furnace computer must send to the Supervisor
after power is first applied is the power-up clear command:
Host sends: >00AA1cr
Supervisor Acknowledgment: Acr
4. The furnace can now send the exhaust set point.
Host sends: >01S010099A28cr
Supervisor Acknowledgment: Acr
5. The furnace can now poll the actual exhaust pressure measurement on a
periodic basis (once per second, for example).
Host sends: >01L00016Ecr
Supervisor acknowledgment: Axxxxyycr
where xxxx will be the measured exhaust pressure, yy will be the checksum
and cr is the carriage return character.
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