User`s guide

17
CP/M BOOT ROM
The CP/M boot ROM sits in ROM page 4.
REMEMOrizer provides this ROM unless you press SW1. So to bypass booting to CP/M, press this
switch whilst resetting the MTX.
(Refer to Chapter 3, Installation, to identify the position of switch SW1.)
It is different to the version found in an FDX or found in an SDX with CP/M support, and is pretty
much the same as the REMEMOTECH version.
The CP/M Boot ROM is broken into a number of modules.
The AZMON module is the initial monitor. It is modified to boot F:52, B:18, B:19, ..., B:1F.
Drives B to 1F are the 8MB SD card partitions and have the same disc configuration
Drive F is configured as Type 52 – 320KB RAM disc
It always loads the RAM Disc support, whether you boot from it or not.
The ASDXKBD module is the keyboard driver. This is the same driver code used in REMEMOTECH,
which queries the CPU clock divider by reading a port. On REMEMOrizer, that port always returns
the value for 4MHz.
ACRT is the 80 column card driver. This has been modified so that it knows that the REMEMOrizer
screen buffer has 4096 character cells (rather than the 2048 in a normal card). It also supports a new
80x48 mode as well as the 80x24 mode. It provides new escape codes ^[Y and ^[Z to switch into
80x24 or 80x48 mode.
ASDCARD is the replacement for the usual floppy disc driver code found in normal Memotech FDX
and SDX systems. It supports a single 8MB size of disk, but through the use of 8 drive type codes
(18..1F) allows you to access 8 8MB partitions of the SD Card.
The SD Card hardware turns on a green LED when the SD Card is accessed and flashes it for a
couple of seconds afterwards, and the user should not remove or change the SD Card until it goes
off. The driver reads a port which tells it that the card was accessed in the last second, and if so, it
can assume that whatever sector it read last is still what it would get if it read that sector again. In
this way, sequential reads of N 128 byte sectors only result in N/4 512 byte block reads (instead of N
512 byte block reads). Also, sequential writes of N 128 byte sectors only result in N/4 512 byte block
reads and N block writes (instead of N 512 byte block reads and N 512 byte writes). This feature
produces a measurable speed increase, perhaps as much as 2x.
The ARAM module provides RAM Disc support. It is a subset of the SIDISC module in the original
Memotech computers, which supported Silicon Disc and RAM Disc. 256KB type 50 RAM Discs are
supported. 512KB type 51 RAM Discs are not supported - there isn't enough memory. A special
320KB type 52 has been defined so as to make full use of the memory available on REMEMOrizer.
Conveniently this exactly matches the type 03 floppy in size and geometry.
ARAM is present in memory, whether you boot from RAM Disc or not. There is no need for a
SIDISC.COM program.