PROCCLK (processor clock) is an output clock for the 80386sx processor.
PROCCLK can be set (with internal configuration register 46H, bits 3-2) for the
following values:
°
PROCCLK = CXIN
°
PROCCLK = CXIN/2
°
PROCCLK = CXIN/4
°
PROCCLK = CXIN/8
PROCCLK can also be halted in order to implement power management techniques.
The effective speed of the 80386sx is always half the PROCCLK frequency; e.g. for an
80386sx speed of 20MHz, PROCCLK must be 40MHz. PROCCLK is derived from an
external crystal oscillator connected to CXIN.
BUSCLK (bus clock) is an output clock for the I/O channel. BUSCLK can be set
(with internal configuration register 41H, bits 3-2) for the following values:
°
BUSCLK = CXIN/4
°
BUSCLK = CXIN/5
°
BUSCLK = CXIN/6
The PROCCLK selection does not affect BUSCLK in either run or sleep modes.
OSC2 (oscillator) is a 14.31818MHz output signal used by the I/O channel. The
oscillator can be derived from an external crystal connected to pins OSC1 and OSC2,
or from an external oscillator connected to OSC1 (leaving OSC2 unconnected).
DMACLK (DMA clock) is an internal clock used by DMA controllers to time DMA
operations. DMACLK can be set (with internal configuration register 01H, bit 0) to
the following values:
°
DMACLK = BUSCLK
°
DMACLK = BUSCLK/2 (AT-compatible)
SYSCLK (system clock) is an internal T-state clock used by 82C836 logic. The
frequency of SYSCLK is always PROCCLK/2.
System Reset and Clock Synchronization
SCATsx supports several different reset signals:
PWRGOOD is the main hardware reset input to the 82C836.
XRST is the main hardware reset output from the 82C836. It resets everything except
the CPU.
CPURST is the CPU reset signal generated by the 82C836. It resets only the CPU.
-RESET2 (MFP3) comes from the 8042 keyboard controller and triggers resetting of
the CPU only (CPURST).
I
System Reset and Clock Synchronization
Clock/Bus Control
4-2
Revision 3.0
P R E L I M I N A R Y
Chips and Technologies, Inc.