Hayes Modem [02/02]

A big hello to you, dear Vasya!

Continuation...

from the ZXNEWS newspaper, issue 15:

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So, what do we see? There is no need to be alarmed if it is written that there is a scheme for coordinating the modem and Scorpio. The fact is that for non
Scorpio the circuits shown in Figure 2
do not need to be assembled at all. And in Fig. 3 the modification is indicated so that the shadow service monitor works. If you want the magic button to work on your Pentagon, you
will have to make this modification. But, as it seems to me, no one has been using magic for a long time and its loss for non-scorpionists will be small. Let's take a look at the diagram. Pay attention to the input and output signals. You won't see anything Scorpio-like. These are ordinary signals
Spectrum.

From top to bottom:

/RD - 21 pin Z80
A4 - 34 pin Z80
/IORQ - 20 pin Z80
/WR - 22 pin Z80
A11 - 7 pin Z80
/Reset - 26 pin Z80
/NMI - 17 pin Z80

Oh yes... The question of flashing the ROM remains open... This is a little more complicated.
But, if there is someone with a programmer who can flash the 27512 with the Pentagon firmware to the same, but with
a corrected byte in BASIC-48, that is, judging bythree-volume ZX-Review 'Programming in Assembly Language', p. 108, third paragraph from the top: "... fix an error in the standard program. To do this, you need to replace code 020H (JP
NZ, ) with code 028H (JP Z, ...) at address 006DH..." After that
you have nothing left. It won’t hurt to connect the modem to your Pentagon or Leningrad.
Go ahead and see you in the vastness of the vast computer world called Fi-
doNet.

With all sorts of regards and wishes.
Igor.

P.S. If you still doubt that
Pentagon + modem is not possible, remember
the author of the scheme, the one who was the first
to connect an internal modem to his
computer, also had only
Pentagon-128...

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From the editor: the connection diagram for Scorpio can be simplified...

(c) Alexander Mayorov
──────────────────────────

Instead of the circuit in Fig. 3:

6th pin 555LL1 (to the modem controller)
is supplied to contact b14/MNI of the system connector through a 300...600 Ohm resistor.

Instead of the circuit in Fig. 2:

another
m/s is installed on the controller board: 555LP8
┌──┐
1│ │3
A4 >───┤ O──────>a13/IORQCE
│ │ on system
+5v───┤ │connector
2└──┘

And the remaining elements can be used
as inverters instead of m/s 555LH1, and the
555LH1 itself can be removed...

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VN> Always yours Vasya

Best wishes, Arno from Omega group.