DESCRIPTION AND OPERATION
MODULE DESCRIPTION
I-E96-308A
2 - 5
channel, the 16-bit count value in output memory for that
channel is transferred into an output buffer comprised of two
output memory buffer chips.
The output buffer is enabled at the appropriate time to place
the count value into the expander bus. If the operation is a
reset-read, after transferring the count value, the buffer clears
both the count memory and the output memory for that chan-
nel. The count will be flagged as invalid if the count is not com-
plete. The count will not be valid until at least one input pulse
is complete, but will always be valid by the end of the second
pulse.
Mode Memory
The mode memory stores the information that determines how
each input is to be handled. Each input can be set for one of
three modes: totalization, frequency or period. The mode for an
input can be set so that the circuitry counts on either the ris-
ing or falling part of the signal. The frequency mode can be set
for three ranges and the period mode can be set for one of six
ranges.
The mode memory occupies one-half of an 8 x 16 memory
array. The other half is the data valid memory. The array stores
the information here necessary to decide if the data valid bit
should be set or not.
Sequencer
Three programmable array logic integrated circuits (ICs) make
up the sequencer. The sequencer is the control center for the
DSM. It provides all the timing signals needed by the other cir-
cuit blocks.
Inputs
Digital field inputs are voltages of either 4 to 6 VDC, 21.6 to 27
VDC, 50 millivolts and 10 Volts (peak to peak). These voltages
indicate an energized (ON) field device; a 0 Volt input indicates
a de-energized (OFF) field device. Jumpers on the DSM select
the voltage level and debounce for each input. The Installation
section explains the jumper connections.
Input Section
The field inputs connect to the termination unit. It sends them
through the termination unit cable to the P3 edge connector on
the DSM. Each of the eight input channels can be set to one of
two possible modes. A third mode is possible for channels 1
and 2. Inputs may be routed to preamplifiers on the DSM to
sense low level signals. The Installation section covers the spe-
cific connections needed for each mode.
