16 Nov
2008
16 Nov
'08
12:30 p.m.
I came across something strange that I need some help with. Pictures
are here:
http://www.brutman.com/2008_1117_140718_RS232_conv_back.jpg
http://www.brutman.com/2008_1117_140718_RS232_conv_top.jpg
It looks like a converter box that takes TTL level serial signals and
converts to RS232 levels, kind of like the MAXIM single chip solution
except that it is using 1488 and 1489 chips.
The problem is that it came with a PCjr, but it doesn't physically plug
into a PCjr. The onboard serial port is only 16 pins, while the
rectangular connector here is 20 pins. It physically doesn't work.
Does anybody know another machine or card that might have used the 20
pin header for a serial port? I'm almost thinking that I'm missing
another piece (a card internal to the machine) that the header goes to.
Regards,
Mike
16 Nov
16 Nov
12:34 p.m.
Michael B. Brutman wrote:
I came across something strange that I need some help with. Pictures
are here:
http://www.brutman.com/2008_1117_140718_RS232_conv_back.jpg
http://www.brutman.com/2008_1117_140718_RS232_conv_top.jpg
It looks like a converter box that takes TTL level serial signals and
converts to RS232 levels, kind of like the MAXIM single chip solution
except that it is using 1488 and 1489 chips.
The problem is that it came with a PCjr, but it doesn't physically
plug into a PCjr. The onboard serial port is only 16 pins, while the
rectangular connector here is 20 pins. It physically doesn't work.
Does anybody know another machine or card that might have used the 20
pin header for a serial port? I'm almost thinking that I'm missing
another piece (a card internal to the machine) that the header goes to.
Regards,
Mike
Might be TTL/232 converter for a HAM rig, specifically Kenwood TS-930 or
'940.
2:10 p.m.
It looks like a converter box that takes TTL level
serial signals and
converts to RS232 levels, kind of like the MAXIM single chip solution
except that it is using 1488 and 1489 chips.
OK, such things did exist.
The problem is that it came with a PCjr, but it doesn't physically plug
into a PCjr. The onboard serial port is only 16 pins, while the
rectangular connector here is 20 pins. It physically doesn't work.
And the PCjr serial port is at RS232 levels anyway. The PCjr seiral cable
is just a cahle, no intenral componnets (I have the PCjr TechRef with
schematics...)
If it was used wit ha PCjr, then I would guess that the PCjr was
connected to the RS232 side of this coverter, and some other device,
using a TTL level serial port, was connected to the 20 pin header.
I can't think fo anything offhand that would have such a port. It might
have been something very specialised (say to control or program some
measuring instrument or something).
-tony
3:20 p.m.
Tony Duell wrote:
And the PCjr serial port is at RS232 levels anyway.
The PCjr seiral cable
is just a cahle, no intenral componnets (I have the PCjr TechRef with
schematics...)
Good point - I'm looking in the TechRef and see that now too. I don't
know why I was assuming TTL logic levels.
If it was used wit ha PCjr, then I would guess that
the PCjr was
connected to the RS232 side of this coverter, and some other device,
using a TTL level serial port, was connected to the 20 pin header.
I can't think fo anything offhand that would have such a port. It might
have been something very specialised (say to control or program some
measuring instrument or something).
-tony
Still clueless. The RS232 side of this device is male, and the serial
adapter cable for a PCjr is also male, so it would have needed a gender
changer to work in that arrangement.
Can I throw something stupid out here? I'm making an assumption that it
was for the serial port. However, if it's just converting voltage
levels is it possible that it was driven by the parallel port? That's
TTL level. (I have no idea what they were attaching to the other side ..)
Mike
17 Nov
17 Nov
10:55 a.m.
Still clueless. The RS232 side of this device is
male, and the serial
adapter cable for a PCjr is also male, so it would have needed a gender
changer to work in that arrangement.
Well, DB25 gender changers are not uncommon ;-)
Now, the IBM serial cable would certainly be wired as a DTE, output on
pin 2, input on pin 3. How is this mystery box wired (can you trace from
the DB25 plug to 1488s and 1489s?)
Is there anything else in the nnit apart from 1488s and 1489s and PSU
parts? Any logic?
Is there any maker's name on the unit or on the PCB?
Does it look to have been commerically soldered or hand-made? SOmebody
else suggested it was used to program a ham radio transceiver, it may be
something that a radio ham built himself.
Can I throw something stupid out here? I'm making an assumption that it
was for the serial port. However, if it's just converting voltage
levels is it possible that it was driven by the parallel port? That's
TTL level. (I have no idea what they were attaching to the other side ..)
I think it's unlikelt. The PCjr doesn't have a parallel port as standard,
if you added one (a 'sidecar' module), it had the normal IBM PC-like DB25
socket on it, same wiring as a PC printer port.
And why would you want to convert that to +/-12V levels? OK, one of the
autodialer interfaces was essentially that (4 data lines, strobe, various
call-progress lines), but did _anyone_ use those with PCs?
No, I think it's more likely that it connected to an RS232 port on the
computer side, and the TTL level side went to some unknown device.
-tony
2:24 p.m.
On 17 Nov 2008 at 18:55, Tony Duell wrote:
Is there anything else in the nnit apart from 1488s
and 1489s and PSU
parts? Any logic?
Is there any maker's name on the unit or on the PCB?
Tony, from the photos, it's a homebrew, built on a piece of
protoboard with hand wiring between the pads. No other logic, just
1488/89 ICs, which means that a supply of +/-12 or so had to come
over the cable.
Being homespun, it's hard to say what this might fit, although a
serial adapter for an early printer (the Epson MX-80, for example,
was sold with only the parallel adapter, even though serial comm
logic was present. The "serial" board was pretty much just level-
shifting to RS-232 levels.
Cheers,
Chuck
18 Nov
18 Nov
11:34 a.m.
On 17 Nov 2008 at 18:55, Tony Duell wrote:
Well, that it curious. I would have thought very few devices had +/-12V
supplies and a TTL level serial port (given the former, adding the
buffers to RS232 is trivial and cheap, and makes the device a lot more
useful).
Is there anything else in the nnit apart from
1488s and 1489s and PSU
parts? Any logic?
Is there any maker's name on the unit or on the PCB?
Tony, from the photos, it's a homebrew, built on a piece of
protoboard with hand wiring between the pads. No other logic, just
1488/89 ICs, which means that a supply of +/-12 or so had to come
over the cable.
Being homespun, it's hard to say what this might fit, although a
serial adapter for an early printer (the Epson MX-80, for example,
was sold with only the parallel adapter, even though serial comm
logic was present. The "serial" board was pretty much just level-
shifting to RS-232 levels.
I beleive there were actually 2 serial adapters for Epson dot matrix
printers. One was just buffers, fonfig switches, and minimal logic. I
_think_ the serial port was bit-banged on one of the printe
microcontrollers, I don;t think said microcontroller has a hardware UART.
The other serial interface contained a microcontorller and buffer RAM,
and was essentially an RS232->Centronics interface.
I guess there were +/-112V supplies on the intenral interface connector
of the Epson printer. But I think you had to add some configuration
switches (which IIRC were read over the port normally used for Centronics
data ioput) to make it useful. So I dout that's what this device is for.
As an aside, somewhere I have what appears to be a GPIB interface board
for an Epson dot matrix printer. I must dig it out and try it...
-tony
12:56 p.m.
On 18 Nov 2008 at 19:34, Tony Duell wrote:
Well, that it curious. I would have thought very few
devices had +/-12V
supplies and a TTL level serial port (given the former, adding the
buffers to RS232 is trivial and cheap, and makes the device a lot more
useful).
I don't recall, except that I constructed a serial interface for an
MX-80 (might have been FX-80, I don't remember) and used a 6 v photo
battery to provide the negative signal levels for handshaking. It
was very simple and I may have picked up the circuit out of one of
the magazines of the time.
I believe that the IBM O&A has a schematic for at least one of the
Epson printers. That might provide some hints if anyone's curious.
Cheers,
Chuck
1:58 p.m.
Which Radio Shack products had a TTL level serial port?
The "boss" at the Radio Shack "Computer Center" said that they did,
indeed, have "Radio Shack 232C" ports.
11:47 a.m.
> Which Radio Shack products had a TTL level serial
port?
On Wed, 19 Nov 2008, Tony Duell wrote:
Something fairly obscrue?
I know the M1, M3, M4, M100, all the CoCos (and the deluxe RS232 pac for
the COCO), PC2 had the proper voltage levels. I assume the M2/12/16 did too
According to doctor Marty, the Tandy portable disk drive is serial TTL
(He says that there are diodes and resistors inside the DB25 hood of the
"special" cable)
11:15 p.m.
According to doctor Marty, the Tandy portable disk
drive is serial TTL
(He says that there are diodes and resistors inside the DB25 hood of the
"special" cable)
Quite possibly. It was intended to be used with the M100 series only,
IIRC, and those machines had RS232 receivers (1489s) that would accept TTL
levels. I will admit that I've driven such RS232 ports directly from TTL
outputs for quick kludges on my bench, but never for anything I expect to
be used by others (I have no way of knowing what sort of port it is going
to be linked to).
I've seen several RS232 peripherals, including the Dowty Quattro modem I
used to use (back when 2400 bps [1] was fast) which take RS232 signals,
feed then through resistors straight into 74HCT inputs, relying on the
protection diodes of said inputs to clamp the signal. It clearly works,
but I don't like it, and would never do it myself.
-tony
20 Nov
20 Nov
5:26 a.m.
New subject: keypunch equip on govliquidation
large govliquidation lot auction opened today has two types of keypunch consoles, one of
which seems to be unused IBM equip. Photo shows it even has some documentation.
http://cgi.govliquidation.com/auction/view?id=2037010&categoryId=c7149
7:43 a.m.
New subject: keypunch equip on govliquidation
In article
<112020081326.28067.49256593000ACD3500006DA322218865869B0A02D29B9B0EBF9D0A050E039A089C
at att.net>,
shumaker at att.net writes:
large govliquidation lot auction opened today has two
types of keypunch consoles
, one of which seems to be unused IBM equip. Photo
shows it even has some docum
entation.
That looks like the kind of keypunch we had at the University of Delaware
around 1979/1980. I remember using them to duplicate punched cards just
for the purpose of making confetti :).
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