"The System 1 Monitor is contained in two fusible link
PROM's (74S571) is very easy to use and provides the following facilities using
one of the 8154 devices as a keyboard interface and display driver:
Reset
initialises the computer after switch on. Memory alter and examine, the
address and data content at any location may be examined and/or rewritten
after this command, and the monitor will recall the address used with this.
Go, starts
execution of program from desired address.
Break-point insert/remove, allows setting and
cancellation of break-point anywhere in memory at which time all internal
registers can be displayed or a user service routine can be executed.
Restore,
allows continuation in original environment of program after break.
Save to tape,
transfers memory contents between given locations on to tape.
Load from tape
loads data into locations specified by the first two bytes on tape.
Display indicates data transfer during loading and reverts
to reset on successful completion.
The monitor provides a number of useful subroutines which
can be inserted in user programs and includes a character font for seven segment
representation of the complete ASCII character set.
The System 1 is provided with a Users Manual which includes
an introduction to binary numbers, descriptions of the 6502 internal
architecture and Acorn hardware, a listing and explanation of the instruction
set and monitor program and a step by step introduction to machine code
programming complemented by 16 original applications programs.
Source code (ca65 format)
The Monitor program is only 512 bytes so if loaded into an EPROM there is space to spare, I have a build, for a 4K EPROM, which includes all the applications listed in the Acorn System 1 User Manual and Teletext Board Technical Manual with some other useful programs:
Source code (Issue 2) (ca65 format)
I have updated the applications, some fixes and extra programs, here is the original for those that already have it blown into an EPROM (e.g. Centre for Computing History's System 1 Trainers).
Source code (Issue 1) (ca65 format)
Note that the original System 1 User Manual was rife with errors so there is no guarantee that all the applications work correctly though I have fixed all the errors that I have found.
I have also created individual assembler listings for these applications and converted them to .wav format using a Python tool I've called bin2wav, they can then be 'played' from a PC straight into your System 1.