INMC 80 News

Nascom Crisis

Dear Sir,

The Nascom crisis is a disappointment – this is just to say I appreciate your work and hope that INMC80 can continue. I only joined a few months ago but the two newsletters were well worth the subscription (particularly as the contents are not available elsewhere).

Mike Whitehead
Dundee University.

Space Invasion Mods ?

Just a few words of thanks for the trouble you are taking to keep the magazine going after all the developments at Nascom and lots of good luck for the future. Please keep the “Kiddies Guide To Z80 Assembler Programming” by Mr. D.R. Hunt going for all us beginners (ME).

I purchased “Space Invasion” by G. CLARKE from the library, can you tell me what changes are needed to run on my N2 under NAS-SYS as this will save me much money at the local amusement arcade ? (Hd. Mr Clarke ?)

Yours, a frustrated programmer,
R.K.Hansell,
Kilwinning, Ayrshire.

Newbear Cassette Interface and Pascal

Dear Sir,

I have just received Issue 1 of INMC News 80 (or THE RETURN OF THE INMC!). I hope that this is not the start of a long series (Son of INMC, INMC rides again etc etc). On reading it, a few points could do with expansion or clarification, hence this letter.

Mr. Keneally’s review of the Newbear/​Cottis-Blandford cassette interface may serve to introduce others to the joys of high speed cassette loading. I have been using the C/B interface for 18 months now at 1200 Baud with astonishing reliability, and have built three units in total (two for myself, one for a friend) all of which work very reliably. There are one or two points which may help Mr. Keneally achieve reliability. In the ACC Newsletter Vol.16 No.5, dated December 1978, Bob Cottis points out that for high mains hum, either the input capacitor can be reduced to about 10nF, or a 1K preset placed between 5v and ground, with its slider taken to the amplifier side of the input capacitor. This preset should be adjusted so that with no input signal the schmitt trigger is in the middle of its hysteresis band i.e. midway between the two points at which the schmitt changes state. I have done this on all the boards I have made, set the frequency of the 555 i.c. with a frequency meter, and they can all read each others tapes very reliably. One other point on this board: The Nascom uses the same clock for receive and transmit, but the C/B board does not. The transmit clock from the C/B is selected by the rate selector option. The receive clock is slow running, and is pulled up by the phase locked loop to match the receive clock demanded by the incoming data.