DESCRIPTION AND OPERATION
DESCRIPTION
2 - 2
I-E96-207A
®
•
Analog to digital (A/D) conversion. It changes analog inputs
to digital values the COM can process.
•
Digital to analog (D/A) conversion. It changes the COM dig-
ital values to analog voltage or current signals to control
process field devices.
•
Accepts digital field inputs, and isolates the module cir-
cuitry from the process.
•
Outputs digital signals to process field devices, and isolates
the module circuitry from the process.
The following sections will detail each of these functions.
Microprocessor
The heart of the controller module is a 68B09 microprocessor
operating at two MHz. The microprocessor is responsible for
memory control, input/output circuitry, serial interfaces, the
machine fault timer (MFT) and self-check routines. The proces-
sors operating system instructions and the function code
library reside in the read only memory (ROM). Since the pro-
cessor is responsible for overall operation, it communicates
with all functional blocks. The processor also does one other
critical task. It constantly triggers the Machine Fault Timer
(MFT) circuit. If the processor or software fails and the MFT is
not reset, the MFT issues a board-wide reset and the Status
LED turns red. This condition is known as a fatal error.
Clock/Timer
The eight megahertz clock provides the clock signals for the
module. It provides the two megahertz clock for the micropro-
cessor and supplies the clock signals for the module system
timer for uniform control algorithm execution.
Status LED Indicator
A front panel module status LED indicator shows the operating
state of the COM. Circuits on the COM determine the module
status and light the LED. The operation section explains the
indications and the troubleshooting section explains corrective
actions to take.
Memory
There is 48 kilobytes of ROM, 4 kilobytes of RAM and 2 kilo-
bytes of battery-backed RAM (NVRAM). The ROM holds the
operating system instructions for the processor. The RAM pro-
vides temporary storage and a copy of the users configuration.
The battery-backed RAM (NVRAM) holds the users configura-
tion (control strategy designed with function codes). It is
