DESCRIPTION AND OPERATION
SLAVE EXPANDER BUS
I-E96-301B
2 - 5
socket empty or not connecting the MMUs with cables sepa-
rates them.
Slave Expander Bus Interface
The IMASI03 uses a custom gate array for the slave expander
bus interface. An integrated circuit holds all the control logic
and communication protocol. This integrated circuit provides
these functions:
•
Address comparison and detection.
•
Message decoding and translation.
•
Data line filtering of bus signals.
•
On-board bus drivers.
•
Expander bus watchdog.
A dual port RAM (DPRAM) stores data that can be accessed at
the same time by the MFP and the slave's microcontroller.
Data Values
For all inputs, channel values are adjusted based on the fac-
tory calibration and drift correction data. Thermocouple inputs
receive cold junction reference compensation. Nonlinearity and
lead wire resistance adjustments are performed when neces-
sary. The IMASI03 slave provides drift-corrected values to the
MFP master over the slave expander bus. These values are in
engineering units.
The slave sends a status indication to the MFP master for each
input channel. This status indicates any hardware errors and
channel configuration errors detected by the slave.
Termination Units
The IMASI03 uses one NTAI06 termination unit or two NIAI05
termination modules to connect to field signals. An NKAS01/
11 cable connects the termination unit to the slave through the
P3 connector. An NKAS02/12 cable connects the termination
module to the slave through the P3 connector. The termination
devices contain RTDs used for cold junction compensation of
thermocouple inputs. They also contain the circuitry needed to
convert 4-20 mA field signals into the 1-5 V needed to input to
the slave. The system power supply is protected from short cir-
cuits by current limiting resistors on the NIAI05 (hardware
revision A) and by fuses on the NTAI06 and NIAI05 (hardware
revision B).
Function Codes
Function codes 215 and 216 in the master MFP configure the
IMASI03 and identify the active analog inputs. One function
code 215 is required for each IMASI03 slave. One function code
216 is required for each input channel used on the slave. These
function codes specify the slave expander bus address of the
