THEORY OF OPERATION
FCS MODULE CIRCUITRY
I-E96-314A
2 - 7
Module Status
The module status block handles all module status messages
from the MCU and holds them in a buffer on the slave
expander bus interface for the processor module to read. The
three module status bits are data available, data loss and
watchdog timeout.
Data Available
The MCU sends the data available status bit to the module sta-
tus block when it has data for the MFP. When the MFP reads
the status block and sees the data available bit set, it can send
a data request to the FCS.
Input Loss
The MCU communicates to the status block that the input sig-
nal is lost. The MFP knows that there is no data available when
it reads this status bit. The input signal may be temporarily
lost when an abrupt change in the input signal frequency
occurs or the input frequency drops below 1 Hz. Operation
returns to the beginning of the process cycle and repeats until
the MCU recovers the signal.
Watchdog Timeout
This status bit warns the MFP of a MCU failure. The watchdog
timer constantly monitors the 20 millisecond clock from the
MCU. The status bit is set when the clock fails to reset the
watchdog timer.
Slave Expander Bus Interface and Address Buffer
The slave expander bus interface block provides the circuitry
that enables communication between the processor module
and the FCS. A Bailey designed integrated circuit provides a
data bus for interfacing the storage area and the module status
buffer to the processor module. This block follows the Bailey
designed protocol for master/slave communications. It per-
forms address compare, R/W strobe generation and contains
bus drivers and receivers.
The operator selects the slave expander bus address by setting
a dipswitch on the FCS. The address byte precedes every data
transfer between the FCS and the MFP. The slave expander
bus integrated circuit enables the address buffer and does an
address comparison before allowing data to transfer to the
slave expander bus. If the addresses match, the MFP can
strobe data to the slave expander bus.
