Example 1: If an SCP module has SCALE = 0010b, and CHGAIN
programmable, then when CHGAIN = 0000, the channel has unity gain
(SHIFT = 0). When CHGAIN = 0001b, the channel has a gain of x4
(SHIFT = 2). When CHGAIN = 0010b, the channel has a gain of x16, and
so forth.
Example 2: If an SCP module has SCALE=0000b (fixed), since SHIFT is
always zero, the SCP module has gain permanently fixed at unity for all
channels.
Example 3: If an SCP module has CHGAIN=0001b (fixed) for all channels;
and if the bottom 3-bits of SCALE are programmable with the sign bit is
fixed at 1. Then the SCP is a programmable attenuator (gain <1.0), and
attenuation is programmed (for the entire SCP) as follows:
Scale
Shift
Function
1000
2
0
unity gain
1001
2
-1
divide by 2
1010
2
-2
divide by 4
1011
2
-3
divide by 8, etc.
Note that the HP E1413 does not support attenuation by greater than 2 (on
standard SCP modules) due to fixed-point arithmetic limits. This does not
prevent SCPs from implementing larger attenuation factors, but such factors
will not work correctly on the HP E1413. Configuring an SCP for a larger
attenuation will cause an error during execution of the
CARDCAL
command.
Note
The Control Processor needs to “ know” the SCP channel gain settings to
properly perform an EU conversion for each channel. The
SCPGAINS
command reads all channel gains and must be executed once the gains are
set and scan lists are defined (see
ASSIGN
and
APPEND
commands).
362 Register-Based Programming
Appendix D
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