From: Bil Herd (bherd_at_ids-business.com)
Date: 2007-04-27 23:14:24
Are you referring to the 14 pin socket next to the LS139? If so, I am going to bet that this was an 74LS02 or something similar. Probably "decoder helper" for the LS139 next to it in the form of programmable invertors (I.E. I invert based on a static need or clock or Address lines). The first TED had very little external decode, no 82S100 type logic that I remember, (which was a 24 or 28 pint chip). We needed to add decode when we needed to latch the keyboard and the banking stuff for function software as we called it. If you were to check you should find that an LS02 should match the connections for inputs and outputs against the way it is wired to the LS139 and to the pull-up resistors next to it. In the "might be a coincidence, might not" department, the C1116 schematic (Thanks zimmers.net) shows the refdes to be U103 and U104 which just might match U3 and U4. Basically the early TED has less devices to talk to so the address map is the same, just less specific about who it's talking to. I say try a TED ROM, it should do something but it wont read keyboard correctly I would bet. Regards, Bil Herd -----Original Message----- From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of Anders Carlsson Sent: Friday, April 27, 2007 8:25 AM To: email@example.com Subject: Re: TED based motherboard Hello again, MagerValp wrote on April 4th: > I played around a bit with flipping bit 3: Now I have received some spare EPROMs and have time in the weekend to play around. Did anyone repair the whole 16K of BASIC ROM, or should I rather burn myself a production ROM for testing? I'll post again if I make some progress. The missing chip in U4 worries me, if it might be a 82S100 type PLA. Based on the ROM dumps, could it be assumed the board has a memory map at least similar to the finshed 264 prototype? Not that I would know how to go on from there anyway... :-) -- Anders Carlsson Message was sent through the cbm-hackers mailing list Message was sent through the cbm-hackers mailing list
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