Zx+Hayes glitches

26 Feb 99 Max Deputat wrote to you here:

MD> The modem is working - I tested it - it worked, but just in case it is USR
MD> Sportster 14400 Fax V.42b internal. 1995 Who can help?

IMHO, buffering will help here.
I have just such a modem connected to this scheme now.
But I am sure that any normal modem will work perfectly with it, although
I personally have not conducted any experiments!

╒═════════ MK_H+buf.W ════════════──

──────────────────────────
Connection diagram of the Hayes modem to the ZX-Spectrum. Standard
Mikhail Kondratiev. On his recommendation,
additional buffering was done.

┌─────────────────────┐ +5V
1533LL1 │ ┌─┐ 3K │ 1533AP6 │
/RD ──────┴─┤1│ ┌─███── +5V │ ┌─┬──┐ ┌┴───────┐
┌─┐ ┌──┤ ├─┴──> IOR (B14) └──1─┤T│ │ │ 8*10K │
A4 ─┤1│ │ └─┘ ┌───19─oE│ │ └┬┬┬┬┬┬┬┬┘
/IORQ─┤
└─┘ │ ┌─┐ 3K D0 ─2─┤ │ ├─18┴│││││││─ D0
└──┤1│ ┌─███── +5V ─3─┤ │ ├─17─┴││││││─
/WR ────────┤ ├─┼──> IOW (B13) ─4─┤ │ ├─16──┴│││││─ m
└─┘ │ / ─5─┤ │ ├─15───┴││││─ o
┌────────┘ SD Z80 - ─6─┤ │ ├─14────┴│││─ d
│ 1533TM2 \ ─7─┤ │ ├─13─────┴││─е
│ ┌─┬──┐ ─8─┤ │ ├─12──────┴│─ м
│ +5V 1─oR│ │ D7 ─9─┤ │ ├─11───────┴─ D7
│ ├─┤ │ └─┴──┘ (A9-A2)
└─────3─┤C│ │ ┌───────> IRQ4 (B24)
A11 ─────────2─┤D│ │ │ ┌─┐
├─┤ │ └1─┤&│ 1533ЛА3
/RESET ─┬─────4─oS│/Qo─6──2─┤ o─3─┐
│ └─┴──┘ └─┘ │
/NMI ─────────────────────────────┘
│
0.047 │ ┌─┐ 3K
╟──┤├──┴───────4─┤&│ ┌─███── +5V
+5V ──███──┬───┬5─┤ o─6─┴────────> RESDRW (B2)
10K │ │ └─┘
│ ─┴─ 0.047
S1 / ─┬─
│ │
═╧═ ═╧═

1533ЛЛ1 3K
┌──┐ ┌─███── +5V
A8 ───1─┤1 ├─3─┴──────> A8 (A31)
┌─2─┤ │ 3K
│ ├──┤ ┌─███── +5V \
A9 ───4─┤1 ├─6─┴──────> A9 (A30) - на модем
├─5─┤ │ 3K /
│ ├──┤ ┌─███── +5V
A10 ──10─┤1 ├─8─┴─────> A10 (A29)
├─9─┤ │
│ └──┘
═╧═

а выходах АП6 показана резисторная сборка - 8
резисторов по 10К подтягивают шину данных модема к +5V.
Кнопка S1 - вобщем-то излишество, но иногда бывает полезна -
можно сбросить модем (если он завис по какой-то причине) не
сбрасывая комп.
Эту схему лучше собрать в непосредственнойproximity to
the modem slot. The length of the wires connecting it to the computer can
reach 50cm (depends on many factors, but, of course,
the shorter the better).

Initiate an interrupt signal on the Z80 like this:

┌──┐ 1533LI1
/NMI from TR-DOS or CACHE ─1─┤& │
/NMI from the modem circuit ─2─┤ ├─3─ to v.17 Z80
└──┘

Felix Knajzev here recommends using 155LI1.
But I don’t know, it should work like that.
──────────────────────────

╘═════════ end of file ════════════──

All the best.
Sincerely, Roman.

RM> IMHO, buffering will help here.
RM> This is the scheme I now have just such a
RM> modem connected to.
RM> But I am sure that any normal modem will work perfectly with it
RM>, although
RM> I personally did not conduct any experiments!
We figured it out (almost ;).
It turns out there was just a miscontact in the connector. The glitch came by accident and disappeared. Science doesn’t know what didn’t connect :)
So, hello, don’t torture the connectors ;D

And you’re right, you need a buffer! I advise everyone who is going to solder this thing. Solder in right away, it won’t hurt :)

Wiz Best wishez, Max Deputat AKA Noizy/PHT.