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1970s architecture ROM chip

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Hi guys and gals,

I was looking through my bag of tricks today full of electronics goodies that I bought on ebay when I wanted to start out in electronics a number of years ago. I saw some interesting parts that i wanted to find out what they were which included triple input NAND chips, Quad AND chips, Octal D transparent latch with edge triggered flip flops. The most interesting part however is a ROM chip that I found where it is programmable and erasable. But not software erasable, the data sheet stated it is erased with a UV light where a full format takes about 20 minutes. The part is a 1024 word 8 bit ROM and it looks, in my eyes, "pornographic"  as Dave Jones would say. I have included some pictures and the link to the datasheet should anyone be interested to look at this beauty. The data sheet is says December 1979, revised 1982 so is the chip from that era or was it built later? Leave a comment below if you know more about the chip. 

Part number is: TMS 2708 JL - 45
Data sheet:       http://www.alldatasheet.com/datasheet-pdf/pdf/125763/TI/TMS2708-45.html


Top view

The beast on her back

Through the looking glass

Just look at all those ball hairs!

Mr Eastwood:

--- Quote ---The data sheet is says December 1979, revised 1982 so is the chip from that era or was it built later?
--- End quote ---

A lot of chips have a 4 digit date-code on them,  so in this case the "8114" is the 14th week of the year 1981;   If you have an older eprom programmer that accepts these you could read the data from it and see what's inside! If you program these, remember to cover the little window up with a sticker to stop it been messed about with in strong sunlight; but not much chance of that here in the UK though ;-)

You are not going to read that with most of the modern programmers, as you need the 12V and -5V supplies to actually get it to work. Drop one and it flat out will not be readable, drop the substrate bias and allow it to drift above 0V and the chip will cook itself. I used them on equipment made in the 1960's, and they were still working 40 years after manufacture with no problems.  I used to have a programmer that handled them, but it was an add on card for an Apple ][ clone.

I love how the datasheet shows how to reprogram it. What would you use it for?  Perhaps on a circuit where you could put predetermined text on a screen if certain conditions are met? For example if a temperature sensor was broken and was linked to a 16x4 screen you could output Sensor 1 failure? Or is this chip used for something entirely different? I have a 0-30v supply but i haven't yet made my own fixed output supply so I should do that next so I can have access to a negative 5v supply.

It is a ROM array, you put in an address to it and it gives an 8 bit output. Mostly used for storing firmware for microcontrollers, and was often used in the early days of computing to perform complex logic, saving having to have 30 TTL chips to do things like change a code from one format to another ( ASCII to EBDIC or to substitute codes for a printer), or to store the initial bootloader so that you did not have to toggle it in via switches on startup, but would turn on the computer and it would automatically load a program in from tape or disk and run it.


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