Hardware Manual - RTD Embedded Technologies, Inc.

With BA + 0x00h, bits 1 and 0 set to 10, load the digital data into the Digital Table. The first digital word loaded
lines up with the first A/D Table entry, and so on:
Entry 1 0000 0000 0000 0000 gain = 1, DM6425HR channel = 1 0000 0000 TMX32 channel = 1
Entry 2 0000 0000 0100 0000 gain = 4, DM6425HR channel = 1 0000 0011 TMX32 channel = 4
Entry 3 0001 0000 0000 0000 skip sample 0000 0000 TMX32 channel = 1 (skip)
Entry 4 0000 0000 0100 0000 gain = 4, DM6425HR channel = 1 0000 0011 TMX32 channel = 4
Entry 5 0000 0000 0000 0000 gain = 1, DM6425HR channel = 1 0000 0000 TMX32 channel = 1
Entry 6 0000 0000 0100 0000 gain = 4, DM6425HR channel = 1 0000 0011 TMX32 channel = 4
Using the Channel-Gain Table for A/D Conversions
After the channel-gain table is programmed, it must be enabled to be used for A/D conversions. Two bits control
this operation. BA + 0x02h, bit 2 enables the A/D Table where the channel and gain data are stored. BA + 0x02h,
bit 3, enables the Digital Table when the digital control data is stored.
Whenever you want to use the channel-gain table, you must set bit 2 at BA + 0x02h high to enable the A/D
Table. If you are also using the Digital Table, you must enable this portion of the channel-gain table by setting
BA + 0x02h, bit 3 high. You cannot use the digital portion without enabling the A/D portion of the channel-gain
table (bit 3 cannot be set high unless bit 2 is also high). When the Digital Table is enabled, the 8-bit data is sent
out on the Port 1 digital I/O lines.
When you are using the channel-gain table to take samples, it is strongly recommended that you do not enable,
disable, and then re-enable the table while performing a sequence of conversions. This causes skipping of an
entry in the table. In this case you should issue a reset table command at BA + 0x00h.
Channel-Gain Table and Throughput Rates
When using the channel-gain table, you should group your entries to maximize the throughput of your module.
Low-level input signals and varying gains are likely to drop the throughput rate because low level inputs must
drive out high level input residual signals.
To maximize throughput:
• Keep channels configured for a certain range grouped together, even if they are out of sequence.
• Use external signal conditioning if you are performing high-speed scanning of low level signals. This
increases throughput and reduces noise.
• If you have room in the channel-gain table, you can make an entry twice to make sure that sufficient
settling time has been allowed and an accurate reading has been taken. Set the skip bit for the first entry
so that it is ignored.
• For best results, do not use the channel-gain table when measuring steady-state signals. Use the single
convert mode to step through the channels.
BDM-610010034 Rev C Chapter 5: A/D Conversions 67