MC68701 Controller
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From: Stefan Huebner on 4 Jun 2010 21:24 Hi all, Does anyone still know the MC68701? It's the EPROM version of the 6801. It offers a Mode 0 which allows for reading and writing the internal EPROM - not like the Hitachi 68xx which can be read and written as 27256 with an appropriate adaptor, this beast needs a monitor program run in mode 0 to work on the EPROM. Now I have one 68701 left with some special code in it and need to reverse engineer the serial protocol it talks (there are some codes sent to another system which couldn't be simulated once we tried, so I need to know which condition leads to sending them). I built a small circuit with the 68701, a HCT573 latch, a 2764 with Motorolas ProBug monitor in it and a HCT138 wired somewhat weird - A12, A14 and A15 go to A,B and C, while A13 goes to /G1, /G2 is grounded and G3 goes to E. Which makes a chip select for B000:BFFF on Y7. But I cannot get the damn thing reading from my EPROM! The data sheet says clearly that in mode 0, the reset vector is BFFE:BFFF. But my 68701 will never read from any Bxxx addresses for a single cycle! Switchhing it to mode 2 or 4 for example works. Opposite to the 6801, which fetches the reset address from FFFE:FFFF also in mode 0 (but then allowing those two addresses to be supplied externally for 2 E-cycles) the 68701 should read from my EPROM on Bxxx. Anyone an idea?
From: Franc Zabkar on 5 Jun 2010 06:38 On Sat, 05 Jun 2010 03:24:15 +0200, Stefan Huebner <stefan(a)huebner-informationselektronik.de> put finger to keyboard and composed: >I built a small circuit with the 68701, a HCT573 latch, a 2764 with >Motorolas ProBug monitor in it and a HCT138 wired somewhat weird - A12, >A14 and A15 go to A,B and C, while A13 goes to /G1, /G2 is grounded and >G3 goes to E. Which makes a chip select for B000:BFFF on Y7. 0xB = 0b1011 Shouldn't A14 and A13 be swapped? - Franc Zabkar -- Please remove one 'i' from my address when replying by email.
From: Stefan Huebner on 5 Jun 2010 07:24
Franc, you are GREAT! I will go and bite my very own a** on monday. I wrapped the circuit together on veroboard somewhen in the evening and now I hope that I actually made the mistake I wrote below. Ten years ago I had some colleagues who would have looked at my circuit, as the one who built it is always somewhat blind. They would have started smiling, tell me, and then we'd have gone for a coffee downstairs at the other workshop. It's about time I start looking for new rooms and some colleagues who work with me. Franc Zabkar schrieb: > On Sat, 05 Jun 2010 03:24:15 +0200, Stefan Huebner > <stefan(a)huebner-informationselektronik.de> put finger to keyboard and > composed: > >> I built a small circuit with the 68701, a HCT573 latch, a 2764 with >> Motorolas ProBug monitor in it and a HCT138 wired somewhat weird - A12, >> A14 and A15 go to A,B and C, while A13 goes to /G1, /G2 is grounded and >> G3 goes to E. Which makes a chip select for B000:BFFF on Y7. > > 0xB = 0b1011 > > Shouldn't A14 and A13 be swapped? > > - Franc Zabkar |