This is an D8755A (pre-programmed with the EITHER the MCS-85+ Resident Monitor or the SDK-85+ resident monitor).

I am making these available for purchase if you can't program the 8755 EPROM for the MCS-85+ or SDK-85+ projects. However, rather than buying this pre-programmed EPROM, another option is to build the Matt Millman Arduino shield project. Details are on his website but for the convenience of my project builders, I have some of his boards for sale here.

Note that the manufacturer, package, date, etc., of the 8755A may not be the same as the photograph.

This resident monitor is specific to the MCS-85+ single board computer OR to the SDK-85+ CPU and the SDK-85+ Key/Display Set.

Details on the resident monitor for the MCS-85+ can be seen in this video starting at about 7:00

MCS-85+ Resident Monitor

The monitor has two modes of operation. The first is in monitor mode where the user is able to give commands to the monitor to display and/or modify processors registers and memory locations. The second mode is when the monitor allows the user to run their program that is also loaded into memory and running on the 8085. Obviously, these two functions are not concurrent. The system boots up in monitor mode and gives the user a prompt at which time the user can issue commands to the monitor. One of these commands is the “GO” command where the monitor turns program control over to the user’s program. The user’s program can return to the monitor by terminating with a RST 0 or RST 1 instruction or through the use of a preset breakpoint. Once the user’s program relinquishes control back to the monitor, the monitor program saves the state of all registers and returns to the monitor prompt. When the user issues the GO command again, the monitor restores all registers (including the program counter and stack pointer) and returns control to the user’s program.

The source code for this monitor is on the project page as well as the User's Manual.

SDK-85+ Resident Monitor The SDK-85+ monitor is the same as Intel's SDK-85 monitor but it has been ported over to this platform. Functionally, it is the same as Intel's v2.1 that shipped with the SDK-85.

The source code for this monitor is on the project page as well as the User's Manual.