Re: Several answers

From: Ethan Dicks (
Date: 1998-03-26 20:57:31

> Hallo Ethan,
> > Traditionally, RS232 was implemented on PETs with either an IEEE488
> > box (I have a couple) or a board that piggybacks into a ROM socket
> > and taps R/W from somewhere (I have an ACIA board like that, too).
> I think I have this IEEE/RS232 interface on paper somewhere, (PET revealed
> page 157) but if it is the right one??? I don't think so. Please tell us at
> least of the used ICs. That could give us some more clues.

I just got it off the shelf: it's a Microtech Portmaker.  The memory map
section of the manual (p13) looks like this:


The ACIAs of the Portmaker board occupy the highest 16 locations of the ROM
socket space where the board is inserted.  For example:

Commodore socket UD11: $A000 thru $AFFF
               ROM     $A000 thru $AFF3
               ACIA U8 (J1) $AFF0 thru $AFF3
               ACIA U7 (J2) $AFF4 thru $AFFF

The actual registers are   ACIA U8 Control/Status  $AFF0
                           ACIA U8 Data register   $AFF1
                           ACIA U7 Control/Status  $AFF4
                           ACIA U7 Data register   $AFF5

The Portmaker itself has an empty ROM socket for the displaced ROM, a 68B50,
an empty socket for another 68B50, line drivers, and for select logic: 'LS21,
'LS393, 'LS30 and an 'LS139

                               _  ___
The three jumper leads go to R/W, IRQ, and Phi2 clock.

As for those IEEE<->RS232 boxes I've got, they are TNW Corp (The Net Works)
TNW-2000 boxes with no CPU, just an AY5-1013 UART, a bunch of TTL/CMOS logic
('LS00, 'LS32, 'LS27, 'LS02, 'LS08, 'LS279, 'LS10, 'LS04, 'LS85, 4049) and
three 3440 IEEE drivers.  The baud rate is controlled by a 555 timer with
externally accessible potentiometer.  There is also an 8-position DIP switch

	1   High  Low      Baud Rate
	2   Even  Odd      Parity
	3   Dis   Enb      Parity
	4   PET   Norm     ASCII
	5   8     0        IEEE
	6   4     0        IEEE
	7   2     0        IEEE
	8   1     0        IEEE

The power rating is unusual: 115/230V 50-400Hz 4W.  I've never seen equipment
rated to 400 Hz before.

One has chips as new as 8310, the other 8009.  The newer one has an AY-3-1015
UART, but is otherwise identical.  I haven't had time to test either one out
since I rescued them from the rubbish bin at Uni (the physics department used
to use PETs).

If I were making one from scratch, I'd probably wire a 6551 onto an adapter
board and stick it in a ROM socket with little or no decoding.  Only when
I was using my PET every day did I worry about how much ROM space I had
(MicroMON, BASIC AID and the ROM PET Rabbit).  I only ever used 8K out of 12K.
Even a dual 6551 board isn't too difficult to wire up, if you clobber the
whole 4K socket.

Speaking of ROMs, BG Micro ( has 2532 ROMs for under $2.  I
just bought a stack to last me probably forever.  They also sell cheap LCD
panels that a PET could drive off the User Port - 4 bits for data and three
control lines.  They'd make great debugging tools.

I have a dream for my Portmaker: in my copious free time, port the C64 PPP
stack to the PET and hook my PET up to the Internet.  If only someone made
an Ethernet card that was easy to hook up to a 6502...


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