Leading Edge Model M
Real-Time Clock Utilities

(c) William C. Parke (1986)

The utilities:

RDCLK.COM
SETCLK.COM

were constructed to read and set the Leading Edge Model M Real-Time
Clock.

Although the DOS supplied with the LE contained a BIOS which
automatically reads and sets the real-time clock (RTC), generic MS-DOS
and PC-DOS is not able to do so, since the RTC support through interrupt
1AH does not follow the standard IBM AT conventions. For this reason,
users who wish to upgrade their LE Model M's to the lastest DOS must
defeat the internal BIOS RTC setting, and run a program like RDCLK once
after booting (which can be automated by putting RDCLK in the
AUTOEXEC.BAT file.) The utility SETCLK can be used to change the date
and/or time of the LE-M RTC by first setting the date-time with the DOS
DATE and TIME commands, then by running the SETCLK program.

To prevent PC-DOS 3.x from scrambling the RTC in the LE-M, unhide the
file IBMBIOS.COM in the root directory of the boot disk. (Save a copy in
case of a mistake in making the following patch.) Use DEBUG IBMBIOS.COM
and search for CD 1A (i.e. Int 1AH. Unassemble the code around the
addresses found (there should be about a dozen). Just before the INT
1AH, there will be moves of a function index into AH. The functions 3
and 5 are intended to set the RTC date and time. These INT 1A
instructions should be patched out by putting two NOPs over the INT 1As.
I found both these locations within the first 4096 bytes in the file.