82C836 Datasheet, PDF (68/205 Pages) List of Unclassifed Manufacturers – Single-Chip 386sx AT

Real Time Clock and Internal Timer Registers
Programmable Interval Timer----8254 Compatible s
Programmable Interval Timer----8254 Compatible
The programmable interval timer, which is equivalent to the Intel 8254 Programmable
Interval Timer/Counter, is programmable through external I/O ports 0040H through
0043H (refer to Figure 6-6).
Figure 6-6. Programmable Timer Control
TMRCLK
(1.19MHz)
VCC
GATE0
CLK0
GATE1
CLK1
OUT0
IRQ0
OUT1
REFRESH-REQUEST
Port 61H bit 0
GATE2
CLK2
OUT2
TONE-GENERATION
Note: All signals shown here are internal to the 82C836.
The inputs of the three channels are connected to a 1.19MHz clock. The 1.19MHz clock
is internally generated by dividing OSC1 (14.31818MHz) by 12. The output of the three
channels are as follows:
• Channel 0 is a general purpose and software interrupt timer. The output of this
channel is connected to the IRQ0 pin of the internal programmable interrupt controller.
• The output of Channel 1 is used internally by the 82C836 to generate refresh requests.
• The output of Channel 2 supports tone generation for the audio speaker.
The Counter/Timer (CTC) in the 82C836 is general purpose, and can be used to generate
accurate time delays under software control. The CTC contains three 16-bit counters
(Counter 0-2) that can be programmed to count in binary or binary coded decimal (BCD).
Each counter operates independently of the other two and can be programmed for
operation as a timer or a counter.
All three counters are controlled from a common set of control logic. The control logic
decodes control information written to the CTC and provides the controls necessary to
load, read, configure, and control each counter. Counter 0 and Counter 1 can be
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