# BASEstartm Open DAS
for Allen-Bradley Data Highwaytm
on Tru64tm UNIX
Installation and User's Guide

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Figure 3-3 shows the structure of a legal Timer or Counter data table address for the PLC-3. Figure 3-4 shows a PLC-3 Timer structure. Figure 3-5 shows a PLC-3 Counter structure.

Table 3-9 shows examples of legal Timer or Counter data table addresses for the PLC-3.

Figure 3-3 PLC-3 Timer and Counter Data Table Address Format

Figure 3-4 PLC-3 Timer Structure

Figure 3-5 PLC-3 Counter Structure

Table 3-9 Example PLC-3 Timer and Counter Data Table Addresses
Example Address | MMS Type1 | Description
--- | --- | ---
$TACC20 | UNSIGNED_16 | Timer 20 accumulated value
CPRE:91 | INTEGER_16 | Counter 91 preset value
TCTL:20/17 | BIT_STRING | Timer 20 Timer Enable bit 2
T20.TD | BIT_STRING | Timer 20 Timer Done bit 2
C5 | Structure 3 UNSIGNED_16 UNSIGNED_16 UNSIGNED_16 | All of counter 5. Control Preset value Accumulated value

1Arrays are not supported.
2Control bits should be treated as read only and modified only under PLC program control. Modifying these bits from a computer can give unpredictable results.
3Write operations are not allowed to structures. Fields in the structure can be any combination of three INTEGER_16 or UNSIGNED_16. The control, preset and accumulated values are read in that order.

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