2-32
2
2.11
I/O CABLE DESIGN
The following instructions will guide the user through the design of an
interface cable between the Digital I/O connector and an external device.
These steps make a three sheet 'A' drawing that can be used to fabricate the
interface cable and a table with the 4807 configuration settings.
1 Make a copy of Tables 2-9 and 2-10 as your worksheets. Use these sheets
when directed to record signals, pin numbers etc.
2. Make a rough determination of the number of output and input signals
from the external device, not exceeding 32 lines.
3. If any of the signal lines are to be monitored, they should be assigned to
the first two bytes, CH1-CH15. (CH16 is not monitored.) The
monitored lines may also be read by a byte or string command.
4. If input data is to be transferred by a string command, assign the external
devices to the data lines starting with first free byte. For BCD/HEX
coding, start with the lowest nibble. Assign the signals to the bit weights
so that the BCD or HEX values are inputted correctly. Any unused lines
must be tied to logic '0' potential. Typical assignments for a small panel
meter are:
I/O Signals:
MSN,
MSN-1, MSN-2, MSN-3
Inputs:
Sign/overrange, MSD, MSD-1, .LSD
Example:
+
1 9 9
Similar bits such as Sign and Overrange can be combined into one four
line group to conserve data lines. Use jumpers to +5 Vdc and to ground
to convert a single line signal such as 'Polarity' into a four bit value. See
the sample cable in Section 2.12 for jumper examples. Tie all unused
data input lines to the logic '0' potential (If the inputs are low true, leave
the unused signals open. The internal pullup resistors will pull the
signals to +5 V). Record the signal names and pin numbers in your copy
of Table 2-9.
5. If output data is being transferred by a string command, the output data
lines should be assigned next. Start with the next available byte in Table
2-9. If the string data is HEX or BCD characters, start with the lowest
available nibble in the byte. If nothing was assigned in step 4, then MSN
