Intel 386 - Manual (Page 95)

Intel386™ EX EMBEDDED MICROPROCESSOR USER’S MANUAL
5-22
Setting bit 0 in the PORT92 register (see Figure 5-14) resets the core without resetting the periph-
erals. Unlike the RESET pin, which is asynchronous and can be used to synchronize internal
clocks to CLK2, this core-only reset is synchronized with the on-chip clocks and does not affect
the on-chip clock synchronization. After the CPU-RESET this bit is still set to 1. It must be
cleared and then set to cause another core-only reset.
Clearing bit 1 in the PORT92 register forces address line A20 to 0. This bit affects only addresses
generated by the core; addresses generated by the DMA and the refresh control unit are not af-
fected.
Figure 5-14. Port 92 Configuration Register (PORT92)
Port 92 Configuration
PORT92
(read/write) Expanded Addr:
ISA Addr:
Reset State: F092H
0092H
XXXXXX10B
7 0
— — — — — — A20G CPURST
Bit
Number
Bit
Mnemonic
Function
7–2 — Reserved. These bits are undefined; for compatibility with future devices,
do not modify these bits.
1 A20G A20 Grounded:
0 = Clearing this bit forces address line A20 to 0. This bit affects
addresses generated only by the core. Addresses generated by the
DMA and the Refresh Unit are not affected by this bit.
1 = Setting this bit leaves core-generated addresses unmodified.
0 CPURST CPU Reset:
0 = Clearing this bit performs no operation.
1 = Setting this bit resets the core without resetting the peripherals.
This bit must be cleared before issuing another reset.