Toshiba T-Series T2200sx, User Manual

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2.6 Timer
An 82C54 equivalent Programmable Interval Timer (PIT) is also included in the SI T9901. The PIT
has three timer/counter channels and its count clock is 1.19MHz. The timer/counters are used to
generate the system timer clock, RAM refresh request, and speaker input. The time-of-day channel
periodically generates the level-0 interrupt request to the central processor. The usage and I/O port
assignments for the PIT are presented in Table 2-4 and Table 2-5.
Table 2-4 PIT channel usage
Table 2-5 PIT I/O ports
Channel Use
0 System Timer
1 Dynamic RAM Refresh Request
2 Audio Signal for Speaker
Port I/O Description
'040' I/O Channel 0 Count Register
'041' I/O Channel 1 Count Register
'042' I/O Channel 2 Count Register
'043' O Control Word Register