80-Bus News


January–February 1984 · Volume 3 · Issue 1

Page 9 of 55

buffering by a 74LS244 whose enables are always tied to 0v. When reading, the /RD signal is used to enable a similar LS244 for buffering the data leaving the card. Assuming that the LS244 is faulty, swapping the two buffers should give an indication of whether this is so. If on power up, all of the RAM appears to contain either all ones or all zeros and no attempt to change them succeeds then replace the LS244. A table of chip numbers for all three RAM cards is given below.

LS244’s used as write buffers:

RAM A card RAM B card Gemini G802

If changing the chip specified doesn’t cure the problem then I can only suggest that the board is returned to the manufacturers via your dealer.


The last bit of what appears to be a takeover bid by me concerns three bits of software that should by this time, be available from Henrys. The first item is about CCPZ. As stated by Dave in a previous issue, there is a bug in all versions (with the possible exception of the Gemini release version) up to V4.1. After this version, CCPZ was made available in Macro-80 source code (hooray) and had the bug fix in it together with an implementation of the “.” command. Since then, another bug has come to light when using SUBMIT files with the GET command. Try typing:


If you get the first command repeated three times then you have the bug. This is because CCPZ changes the default DMA address when getting the requested file and forgets to change it back. The result is that further SUBMIT commands are read to memory above the last file read. CCPZ then checks the default buffer and of course finds the last command which is repeated. With version 4.3, this bug has been fixed and there is no reason why everyone shouldn’t be using CCPZ now. Order yours tomorrow! (No I don’t work for Henry’s).


My second bit of software news concerns a Z80 implementation of the CP/M BDOS, by some strange coincidence, called BDOSZ. In true CCPZ fashion, the space saved by doing the conversion has made room for extra goodies while still retaining CP/M 2.2 compatibility. This package came about as a result of the good fortune of Chris Bellingham of Canterbury, who found a part completed source version of something which would behave rather like the CP/M 2.2 BDOS (author unknown) in an ancient file tucked away in the memory banks of the VAX mainframe at the University of Kent. Chris was at that time running CP/M 1.4 with a second hand Henelec FDC and drives. Being on a students grant, he had never considered the change to CP/M 2.2 as being economically viable. Having found the BDOS and typed the source into his Nascom, there followed a good deal of hard work to finish the BDOS and debug it. Once completed and armed with CCPZ and a home brew BIOS, he had CP/M 2.2 for next to nothing.

At about this time, I obtained a copy for interest value. The error reporting was as Chris originally found it and if possible was worse than that in DRI’s BDOS. Also, at the end of the BDOS was a large unused area which we thought might be able to provide some extra goodies. As Chris was busy, I got the job of upgrading BDOSZ to something that would cure the limitations placed on users by the standard CP/M BDOS.

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