Hi, I am in the process of reverse engineering the Function Board (the thing that scans the keyboard matrix, controls LEDs and sends messages to another board the controls the motors that make the print head move, spins the daisy wheel and rolls the platen. IBM uses ICs with their own part numbers (for everything except the 8031AH). Most of them are just rebadged logic parts. I found a site (https://vintagecomputer.ca/ibm-vintage-logic-chip-equivalency-list/) that converts most of them and I was able to use a minipro and a github project (https://github.com/gstrike/minipro_id_logic) to test and identify another IC. The last one is not a logic chip. It is in a DIP14 package. The chip is marked with a National Semiconductor IC logo, and the IBM part number 849 3328. The date code is 38th week of 1983. The underside of the chip is marked "AT5/VN/R+". The chip is the lower one in the photograph here: https://photos.app.goo.gl/1imtQKtYVfn1ZkwW9
The chip is part of a circuit associated with a battery-backed static RAM. A 3-cell AA battery pack positive terminal goes through a 470 ohm resistor and a diode to VDD. Here is a sketch of the circuit: https://photos.app.goo.gl/Kd1vf38yMe5PToKQA. When the typewriter is turned off, the 5V and 12V go away. Pins 2, 4, 6 and 10 are connected together, but not to anything else (I haven't measured it in-circuit).
Can anyone help my identify the chip?
The chip is part of a circuit associated with a battery-backed static RAM. A 3-cell AA battery pack positive terminal goes through a 470 ohm resistor and a diode to VDD. Here is a sketch of the circuit: https://photos.app.goo.gl/Kd1vf38yMe5PToKQA. When the typewriter is turned off, the 5V and 12V go away. Pins 2, 4, 6 and 10 are connected together, but not to anything else (I haven't measured it in-circuit).
Can anyone help my identify the chip?