27 Jun
2006
27 Jun
'06
5:07 a.m.
I've got some equipment here that has RS422 serial on it - i.e. it uses
differential signal pairs rather than RS232's reference against ground.
Question is, can I wire up a cable so that I can use an RS232 terminal with
this RS422 equipment? (running over a short distance)
Looking at the schematics, I think it's possible, with signals mapping to:
RS422 RS232
RXD- GND
RXD+ RX
TXD- no connection?
TXD+ TX
CTS- GND
CTS+ CTS
BSY- no connection
BSY+ RTS
... but I don't know if I should ground TXD-, or indeed one web site I saw
suggested that TXD- should be used as the signal and TXD+ is actually the
reference. I suspect that one or other should be left floating and the other
pin of the pair forms the 'real' TXD in RS232-speak.
Obviously I need to swap signals for communications to work (RX -> TX, TX ->
RX etc.) :-)
CTS- and BUSY- aren't actually brought out to the comms port on the equipment
at all; CTS- is currently jumpered to ground internally, and BUSY- is left
floating and brought to a test point on the PCB.
RXD- is also currently jumpered to ground, which suggests that I can indeed
connect TX on the RS232 terminal to RXD+ on the equipment and expect that side
of things to work - I'm just not sure what I need to do with the TXD+/TXD-
signal pair (which one actually connects to RX on the terminal end)
(the actual comms chip is a 6551A, then the receiver for RXD and CTS is a
26LS32 and the driver for TXD and BSY is 26LS30)
cheers
Jules
27 Jun
27 Jun
5:12 a.m.
Am 27 Jun 2006 12:07 meinte Jules Richardson:
I've got some equipment here that has RS422 serial
on it - i.e. it uses
differential signal pairs rather than RS232's reference against ground.
Question is, can I wire up a cable so that I can use
an RS232 terminal with
this RS422 equipment? (running over a short distance)
YMMV <- maybe the most apropriate US abrevation :))
It's for shure outside the specs it may or it may not work.
Usualy I'd recommend using a nice 8 Pin Max 3462. It's just 3 Bucks
and will remove a lot of possible debugging. Beside that, your cable
looks fine.
Sill, the 422 Specs define +/- 2 V as low and +/- 6V as high for the
sender side and +/- 0.2V as minimum for receiving circuits.
(the actual comms chip is a 6551A, then the receiver
for RXD and CTS is a
26LS32 and the driver for TXD and BSY is 26LS30)
Use a Max3462
Gruss
H.
--
VCF Europa 8.0 am 28/29.April 2007 in Muenchen
http://www.vcfe.org/
5:36 a.m.
New subject: RS232 <=> RS422 (Add on)
One more:
If you don't want to use a Max3462 a little converter-circuit would be fine:
RS232-EQ
GND -----#------------------------------------------------------- GND
TX -----+------------------------------------------------------- RX-
'------------------------------------------------------- RX+
RX ---, ,--XXXXXXX---------------------------------- TX-
\| | 100 Ohm ,------------------------------- TX-
|-----------# |
*| | |
/ V |
| --- |
| | |
'-------------'-----------'
# -> connection
|
V -> Diode
---
|
Log time since I did Ascii drawings :)
Gruss
H.
--
VCF Europa 8.0 am 28/29.April 2007 in Muenchen
http://www.vcfe.org/
7:10 a.m.
It was written....
I've got some equipment here that has RS422 serial
on it - i.e. it uses
differential signal pairs rather than RS232's reference against ground.
I
haven't seen RS422 in a good while. My first exposure to it was an IBM
Series/1 running Pick. The serial connections were all RS422. I scratched my
head when I opened a cable hood for the first time ;)
Question is, can I wire up a cable so that I can use
an RS232 terminal
with this RS422 equipment? (running over a short distance)
No. I believe RS422 has
most of the signals split as pairs, where the logic
true vs. false is the differential between the two pins rather than a set
level. RS232 will not work with this. It'd be like trying to hook up a
differential scsi device to a non-differential scsi device. A cable mod
isn't going to get you there.
We also commonly saw systems (GA Zebra for one) that used RS423, which was
the same as RS232 except the voltage levels which indicated the logic
levels. I *think* that on RS232 the swing was around 12v, and on RS423 it
was around 4v... something along those lines. It was usually possible to
plug an RS232 terminal into an RS423 port depending on the tolerances in
it's design.
Jay West
8:57 a.m.
Jay West wrote:
We also commonly saw systems (GA Zebra for one) that
used RS423, which
was the same as RS232 except the voltage levels which indicated the
logic levels. I *think* that on RS232 the swing was around 12v, and on
RS423 it was around 4v... something along those lines. It was usually
possible to plug an RS232 terminal into an RS423 port depending on the
tolerances in it's design.
Yes, that sounds about right. It does look like this equipment has an RS423
mode; I just need to work out how to configure it :)
(I've used RS232 devices against RS423 before so I know it *can* work - I
suspect that I just need a healthy +5V supply rail on this intended device so
that it stands a better chance of working)
cheers
Jules
9:13 a.m.
On 6/27/2006 at 12:07 PM Jules Richardson wrote:
I've got some equipment here that has RS422 serial
on it - i.e. it uses
differential signal pairs rather than RS232's reference against ground.
Question is, can I wire up a cable so that I can use an RS232 terminal
with this RS422 equipment? (running over a short distance)
At the expense of stating the obivous, if this involved equipment I cared
about and my time meant something to me, I'd just buy a commercial
converter. Most feature some sort of isolation in addition to level
conversion. E-Pay shows several that run about $20 shipped.
Cheers,
Chuck
3:12 p.m.
I've got some equipment here that has RS422 serial on it - i.e. it uses
differential signal pairs rather than RS232's reference against ground.
Question is, can I wire up a cable so that I can use an RS232 terminal with
this RS422 equipment? (running over a short distance)
This somewhat depends on the drivers/receivers used. The 26LS3x ones
generally will work as you want them to. To do the job properly, I'd use
similar chips to convert the signals back to TTL, then add a MAX232 or
similar.
Looking at the schematics, I think it's possible, with signals mapping to:
RS422 RS232
RXD- GND
RXD+ RX
TXD- no connection?
TXD+ TX
CTS- GND
CTS+ CTS
BSY- no connection
BSY+ RTS
... but I don't know if I should ground TXD-, or indeed one web site I saw
No, leave the 'unused' TxD output unconnected.
suggested that TXD- should be used as the signal and
TXD+ is actually the
reference. I suspect that one or other should be left floating and the other
pin of the pair forms the 'real' TXD in RS232-speak.
Which one you use depends on the convention for labelling '+' and '-'
here. Find the one that's -ve when the unit is idle, and use that.
(the actual comms chip is a 6551A, then the receiver for RXD and CTS is a
26LS32 and the driver for TXD and BSY is 26LS30)
If all else fails, disconnect the RS422 stuff and link a MAX232 or
similar to the right pins on the 6551...
-tony
5:22 p.m.
On 6/27/2006 at 11:12 PM ard at p850ug1.demon.co.uk wrote:
This somewhat depends on the drivers/receivers used.
The 26LS3x ones
generally will work as you want them to. To do the job properly, I'd use
similar chips to convert the signals back to TTL, then add a MAX232 or
similar.
As an alternative to consider, Analog Devices makes a nifty little chip
that's got 422 and 232 drivers and receivers on it, and is +5
powered--AD7306.
http://www.ortodoxism.ro/datasheets/analogdevices/264748104ad7306.pdf
28 Jun
28 Jun
2:45 p.m.
As an alternative to consider, Analog Devices makes a
nifty little chip
that's got 422 and 232 drivers and receivers on it, and is +5
powered--AD7306.
http://www.ortodoxism.ro/datasheets/analogdevices/264748104ad7306.pdf
Looks interesting. I wonder if you can get 1-offs anywhere (I've not
looks yet). On the other hand, the 26LS3x's and the MAX232 are easy to
obtain (even though they take up more board area).
-tony
6:32 p.m.
Looks interesting. I wonder if you can get 1-offs anywhere (I've not
looks yet). On the other hand, the 26LS3x's and the MAX232 are easy to
obtain (even though they take up more board area).
Just looked at DigiKey--you can get them, but I've seen cheaper MPUs! You
could also sample them from Analog.com if your day job qualifies you.
As far as board space, if one were using DIPs, it'd be a hard call. The AD
IC is a 24 pin PDIP (also comes in SOIC).
--Chuck
5:38 p.m.
Looks interesting. I wonder if you can get 1-offs anywhere (I've not
looks yet). On the other hand, the 26LS3x's and the MAX232 are easy to
obtain (even though they take up more board area).
Just looked at DigiKey--you can get them, but I've seen cheaper MPUs! You could also sample them from Analog.com if your day job
qualifies you.
What day job? I doubt if 'privately repairing old HP calculators' counts :-)
As far as board space, if one were using DIPs,
it'd be a hard call. The AD
IC is a 24 pin PDIP (also comes in SOIC).
I'd rather keep buffers that talk to the outside world in
pin-through-hole DIPs, since they're likely to get zapped at some point,
and it's a lot easier to replace a (socketed?) DIP than a SOIC. Anyway,
board area (and component count) are not too important for 1-off
prototype designs IMHO.
-tony
1 Jul
1 Jul
1:50 a.m.
On Thu, 2006-06-29 at 01:38 +0100, Tony Duell wrote:
They don't check *that* hard...
Gordon.
could also
sample them from Analog.com if your day job qualifies you.
What day job? I doubt if 'privately repairing old HP calculators' counts :-)
6515
days inactive
6519
days old
11 comments
6 participants
participants (6)
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ard＠p850ug1.demon.co.uk -
cclist＠sydex.com -
gordon＠gjcp.net -
Hans.Franke＠siemens.com -
julesrichardsonuk＠yahoo.co.uk -
jwest＠classiccmp.org