Rom Subsystem; Ram Subsystem - Datatech Enterprises Apex 386SX/20 User Manual

ROM Subsystem

The ROM subsystem has a 32K by 16-bit arrangement consisting of
two 32K by 8-bit ROM/EPROM modules. The odd and even address
codes reside in separate modules. The top of the first megabyte and
the bottom of the last megabyte address space is assigned to ROM
(hex OF0000 and hex FF0000). Parity checking is not done on ROM.
BIOS has been provided in this subsystem.

RAM Subsystem

The RAM subsystem starts at address hex 000000 of the 16M address
space. It consists of either 640KB or 1MB in the form of 256K or 64K
by l-bit RAM modules. Memory refresh forces one memory cycle
every 15 microseconds through channel 1 of the timer/counter. The
following functions are performed by the RAM initialization program:
Note:
Memory can be used only after being accessed or refreshed eight
times,
Chapter 6: Appendix
20
• Write operation to any memory location.
• Initialization of channel 1 of the timer/counter to the rate
generation mode (15 microseconds).