82C836 Datasheet, PDF (70/205 Pages) List of Unclassifed Manufacturers – Single-Chip 386sx AT

Real Time Clock and Internal Timer Registers
Programming the Counter Timer Controller s
Programming the Counter Timer Controller
After power-up, the conditions of the CTC control register, counter register, CE, and the
output of all counters is undefined. Each counter must be programmed before it can be
used.
Counters are programmed by writing a Control Word and then an initial count. The
Control Register of a counter is written to by writing to the Control Word address, as
shown in Table 6-3. Figure 6-7 shows the Control Word structure. The control word is
a write-only location.
Table 6-3. Counter Timer Control I/O Addresses
Address
040H
041H
Function
Counter 0 Read/Write
Counter 1 Read/Write
Address
042H
043H
Function
Counter 2 Read/Write
Control Word, write only
Figure 6-7. Control Word----Address 043H
B7 B6 B5 B4 B3 B2 B1 B0
___________________________________ __________________________ ________
BCD Binary Coded Decimal
M<0:2> Counter Mode
F<0:3> Command Flag
bits: B0
B1-B3
BCD
M<0:3>
BCD selects binary coded decimal counting format during
Read/Write counter commands. When bit 0 is set to zero, the count
is binary; when bit 0 is set to one, the count is BCD. Note that
during Read-Back command, this bit must be zero.
These three bits determine the counter’s mode during Read/Write
counter commands, or select the counter during a Read-Back
command. Bits 1-3 become ‘‘do not care ’’ during Latch Counter
commands.
Chips and Technologies, Inc.
PRELIMINARY
Revision 3.0 6-1 1