DESCRIPTION AND OPERATION
MODULE BLOCK DIAGRAM
I-E96-303A
2 - 3
determine when the default states should be used. Refer to
BUS FAULT TIMER
in this section for further explanation of
time-out
. The PAL cycles the DPRAM and the S/H circuits
through each output channel. It selects only one output chan-
nel and its corresponding S/H circuit at a time.
Output Logic
Defining Function Code (FC) 149 in the MFP configuration
establishes the output values; this function code defines only
seven outputs. Two function blocks must be linked, using
specification 2 (FC 149), to define all fourteen outputs. The
MFP sends an analog count value to the ASO for each of the
analog outputs. These counts are determined by FC 149.
The ASO sets each output based on its analog count (digital
value); the D/A converter changes this count to an analog sig-
nal that it sends to the S/H block. An analog count from the
DPRAM is held in the D/A register until the D/A converter is
ready for it. The S/H select block is a multiplexer that selects
the appropriate S/H circuit. The selected circuit corresponds
to the current output channel; the output channel and S/H
circuit selection are controlled by the PAL. S/H circuits sample
the analog signal and hold its value while the PAL sequences
through the rest of the channels. During normal operation,
this sequence repeats continuously for each of the output
channels.
Readback Logic
The feedback select block is a multiplexer that selects one of
the output feedback signals or the reference voltages. An A/D
converter changes these signals to analog count values the
MFP reads through the slave expander bus interface. Each
channel is read separately. These values allow the MFP to
adjust the outputs and check for output circuit failures. It does
this by comparing the values against the data written to each
output. Reading the reference voltage count values allows the
MFP to check A/D converter operation.
Default Operation
A
time-out
condition causes the ASO module to go to default
operation. The PAL puts the module into default operation when
it receives a bus fault signal from the slave expander bus inter-
face. Each output goes to its default state (0 percent, 100 per-
cent or
hold
); FC 149 (specifications 11 through 17) define each
output default state. This FC defines only seven channels; two
function blocks must be linked to define all fourteen channels.
The PAL reads default data from the DPRAM to control the out-
put data that is sent to the D/A converter during a bus stall
(
time-out
) condition. A 0 percent option causes the D/A register
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