DESCRIPTION AND OPERATION
MODULE DESCRIPTION
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I-E96-308A
®
Multiplexer and Input State Circuitry
The eight conditioned input signals from the Schmitt-trigger
inverters are time-division multiplexed to use a single 16-bit
counter. A channel counter increments the multiplexer. Each
channel processes in turn every 7.2 microseconds (every 7.8
microseconds if a slave expander bus transaction takes place).
The channel counter spends about 900 nanoseconds process-
ing each input before moving onto the next channel.
When the multiplexer selects a channel, an 8-bit shift register
stores the input state (0 or 1). The register shifts for each chan-
nel sample. The 8-bit register will hold the previous input state
for each complete count. The MFP may read the present input
state.
Time Base Generation
The six time-base signals generated here are multiplexed for
greatest resolution for the sampled input. The choice recorded
in the mode memory determines the time-base signal selected.
Present and previous time-base pulse states are stored for use
in determining count completion.
Slave Expander Bus Interface
The expander bus interface translates the 8-bit bidirectional
expander bus into two 8-bit unidirectional internal busses; one
input and one output. Information is communicated over the
expander bus by sending either three or five bytes in sequence
depending on the operation. The operations that the MFP can
request from the DSM are: read module type status, read input
states, write channel configuration, read channel and reset
and read channel.
The expander bus interface receives an 8-bit module address
from the MFP and compares it to the address set on S1. If the
addresses match, then the module will respond to the bytes
that follow. If the function code byte specifies a read operation,
the interface will send the selected information from the output
buffer.
Count and Output Memory
There is only one 16 bit counter. All 8 input channels share the
counter. A 16-bit memory location stores the count value asso-
ciated with each channel. The memory (count memory) takes
up one-half of a 16 x 16 memory array made up of four RAM
memory chips.
The other half the memory array (output memory) stores the
final or total accumulated count. Whenever the MFP reads a
