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Chapter 10. Configuring the I/O Driver from FIX/iFIX Applications177
Read
Algorithm
Reads from a 3-digit BCD register.
The Raw_value is then separated
into three nibbles (4 bits) prior to
scaling the value. Each nibble is
examined for a value greater than 9
(A-F hex). If a hexadecimal value
between A and F is found, a range
alarm is generated, indicating the
value is not within BCD range. Each
hexadecimal nibble between 0 and 9
is converted to a decimal value and
the resulting BCD value is scaled
with the following algorithm:
Result = ((BCD_value/999) *
Span_egu) + Lo_egu
Read
Algorithm
Variables
Lo_egu – the database block’s low
engineering value.
Span_egu – the span of the
engineering values.
BCD_value – the BCD value
converted from the raw value.
Result – the scaled value stored in
the database block.
Write
Algorithm
Writes to a 3-digit BCD register
using the following algorithm:
Result = (((InputData – Lo_egu) /
Span_egu) * 999) + 0.5
and then converts the resulting value
back to a 3BCD value prior to
sending it to the process hardware.
Write
Algorithm
Variables
Lo_egu – the low engineering value.
Span_egu – the span of the
engineering values.
InputData – the database block’s
current value.
Result – the unscaled value.
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