Letters

Loan Amortization

Dear Editor:

I would like to suggest two changes in the loan amortization program (SYNC 3:1, p. 30):

Add:

124 PRINT
125 PRINT "TOTAL PAID IS:#$";P*MO

Change line 145 to:

145 FOR I=1 TO MO

The “TOTAL PAID” line is useful in comparing two different mortgage programs, e.g., a home loan at 13.5% for 30 years versus 12.25% for 15 years. The change in line 145 makes the amortization chart run with the length of the loan.

Len Parkin
[address omitted]
Summit, NJ

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LOADing Problems

Dear Editor:

I have had periodic trouble with SAVEing and LOADing with my ZX81. I went to a negative ground cassette, thinking that would help. But not too much!

Then I watched the output from the recorder on a scope. As compared with prerecorded tape, my tapes were relatively noisy and errative and slightly fluctuating in audio level. I then opened the recorder and disabled the automatic recording level control.

I have not had the problem since. It gives you a good feeling to see a tape LOAD without a flaw, especially when you work two or three hours programming for a file.

Phil Epp
[address omitted]
Wichita, KS

Ed.—LOADing and RAM pack wobble seem to top the list of problems we hear about. In our next issue we will gather some of the suggestions for dealing with these problems.

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Mazogs

Dear Editor:

I recently acquired the Mazogs game and found it to be one of the best I have yet seen for the ZX81. I did find one minor bug in it though. When the entire maze is displayed at the end of the game, the computer will crash if you scroll the maze past the top or bottom border. This can be remedied by rewriting line 1050 as follows:

1050 LET X=X+(K$="J")-(K$="H")+(K$="S")*64-(K$="W")*64+(X=MST+64)*64-(X=MST+1504)*64

My congratulations to Don Priestly on this excellent game and I will be looking forward to more of his creations.

Glen Martin
Ultimatum
[address omitted]
Abbotsford, B.C.
Canada

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Keeping Time

Dear Editor:

I have received several requests for the seconds indication for the face clock in my article in SYNC 3:1. This is one way to add the seconds, but it requires more than 2K RAM:

230 FOR Q=3 TO 36
231 LET R=Q/23*PI
232 PLOT 27+18*SIN R,22+18*COS R
233 UNPLOT 27+18*SIN R,22+18*COS R
234 NEXT Q
235 PAUSE 166

Another question was how to adjust the timing of the clock. Here is how I do it: Using WWV time or other accurate means, time the clock for a full hour. Then, if it is fast by 7 seconds, for example, add 7 to the PAUSE value. If it is slow by 12 seconds, for example, subtract 12 from the PAUSE value.

Chuck Dawson
[address omitted]
Ft. Worth, TX

Ed.—The author also has developed two machine code clock programs with seconds. These require at least 16K RAM. He will supply them on tape to anyone interested for $10.

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EPROM Programmer

Dear Editor:

I have a ZX81 with a Memotech 64K RAM pack. The Memopak includes 8K RAM which fills the transparent block of memory from 8-16K. Since this area is now occupied, is it still possible for me to use the EPROM Programmer in SYNC 3:1? What, if any, modification is necessary?

John Graf
[address omitted]
Baton Rouge, LA

Dan Schaaf—There is a problem, but because each memory pack probably does things slightly differently (and because I do not have one or a schematic of one), I do not know of a way to make the circuit work without more specific information. In principle, it would be an easy matter. There is a probably a problem also with 32K packs. But I see no problem with 16K packs since they do not address the ROM space. I have also received letters about my pin assignments. I would advise getting the data sheet for the EPROM you buy and then use its pin assignments.