Date: 6/30/22 3:27 PM (GMT-05:00) To: Lars Brinkhoff , B Degnan Subject: Re: Reading a Datapoint 3300 ROM Lars, I have dumped the ROM in the Datapoint 3300, using a PIC and some level shifters. The ROM part number is TMS 2A 4151 MH. It was not in a socket, but I managed to get it out without too much trouble. I am attaching a schematic of the dumping circuit, and also a photo of it. The PIC runs at 5V, and the ROM operates at 12V, so it was necessary to add level shifters to up convert the inputs and down convert the outputs. The PIC reads the data, then sends it over RS-232 to a Windows laptop running Teraterm. I am sending the data in two files. One is an ASCII text file generated by the dump program. It shows the data for each character (5 bytes) using asterisks. An asterisks corresponds to a +12V level coming out of the ROM, which would technically be a 0. That is to say that +12V on the input to the ROM would be a 0 and 0v would be logic 1. I will attach the data sheet for a similar TI ROM for you to look at. The voltage levels can be pretty confusing. The I1 output of the ROM corresponds to the top of the character. This agrees with the TI data sheet. The Datapoint 3300 service manual shows I7 as the top of the character but that is wrong. The second file is a binary file, also generated by the dump program, containing the same 320 bytes (64 x 5) represented by the ASCII text file, and in the same order. The top bit of every byte is 0. The next bit would be O7, then O6, etc. The first 5 bytes correspond to character index 0. They are in the order column A, then column B, etc. The next 5 bytes are character index 1, etc. Let me know if you have any questions about the data. Bob Grieb