5 Apr
2007
5 Apr
'07
4:57 p.m.
Is this online anywhere to anyone's knowledge? I assume it's in the techrefs
[1] (which I don't have, unfortunately), but I'm sure I've seen the schematic
online somewhere in the last few years.
IIRC it's only a handful of latches, buffers and address decoding - so not a
complex bit of hardware.
[1] The circuit on the MDA card is probably the same... if someone could
confirm that then I could at least trace it from a real MDA card here :)
cheers
Jules
5 Apr
5 Apr
8:12 p.m.
On Thu, 2007-04-05 at 10:57 -0500, Jules Richardson wrote:
Is this online anywhere to anyone's knowledge? I
assume it's in the techrefs
[1] (which I don't have, unfortunately), but I'm sure I've seen the schematic
online somewhere in the last few years.
IIRC it's only a handful of latches, buffers and address decoding - so not a
complex bit of hardware.
[1] The circuit on the MDA card is probably the same... if someone could
confirm that then I could at least trace it from a real MDA card here :)
I have it, in the techref, but no scanner until I'm back at work on
Tuesday.
Gordon
9:17 p.m.
Is this online anywhere to anyone's knowledge? I assume it's in the techrefs
It is. It's in Volume 2 of the Options and Adapters Techref at least (I
have it).
[1] (which I don't have, unfortunately), but
I'm sure I've seen the schematic
online somewhere in the last few years.
IIRC it's only a handful of latches, buffers and address decoding - so not a
complex bit of hardware.
Yes, just a few TTL chips, nothing really clever at all.
[1] The circuit on the MDA card is probably the same... if someone could
confirm that then I could at least trace it from a real MDA card here :)
There are minor differences, mainly due to the fact that the MDA card's
printer port is at a different address (you can have the MDA card _and_ 2
printer adapters in the same machine).
Are you in England at the moment? If so, I could probably be convinced to
snail-mail you a copy of the page from the Techref.
-tony
6 Apr
6 Apr
1:16 a.m.
Tony Duell wrote:
Are you in England at the moment? If so, I could
probably be convinced to
snail-mail you a copy of the page from the Techref.
Now sorted out, but thanks anyway (email burp meant I couldn't reply to say I
now have it). Ta to those who offered...
cheers
Jules
9:38 p.m.
Tony Duell wrote:
I had a quick look in my techrefs last night...
The printer port on the MDA card and the separate printer adapter are
much the same logically, but there are differences in the actual
implementation.
For example, the MDA card inverts some of the status lines from the
printer using '04 NOT gates. The printer adapter uses '86 XOR gates (XORs
the siangl wirh '1', basically), presuably because they needed an XOR
gate to selectively invert one of the address lines to give the 1st/2nd
adapter address selection.
-tony
Are you in England at the moment? If so, I could
probably be convinced to
snail-mail you a copy of the page from the Techref.
Now sorted out, but thanks anyway (email burp meant I couldn't reply to say I
now have it). Ta to those who offered... 
10:13 p.m.
On 4/5/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
There are minor differences, mainly due to the fact
that the MDA card's
printer port is at a different address (you can have the MDA card _and_ 2
printer adapters in the same machine).
That's handy to know - every once in a while, I long for a machine
with 2 or 3 parallel adapters, for things like old Connectix cameras,
LCD displays and the like. I've never assembled an ISA machine with
more than one printer adapter. I know that it really doesn't matter
to your own code what the I/O address is, but I wasn't sure how
flexible the underlying hardware might be to being assigned to
alternate addresses.
-ethan
7 Apr
7 Apr
6 a.m.
On 6 Apr 2007 at 17:13, Ethan Dicks wrote:
That's handy to know - every once in a while, I
long for a machine
with 2 or 3 parallel adapters, for things like old Connectix cameras,
LCD displays and the like. I've never assembled an ISA machine with
more than one printer adapter. I know that it really doesn't matter
to your own code what the I/O address is, but I wasn't sure how
flexible the underlying hardware might be to being assigned to
alternate addresses.
2P+2S ISA adapters aren't particularly difficult to find. Some of
them will even support EPP and ECP modes. I seem to recall that
there were 3 "stock" port addresses (3BCh, 378h, 278h), but others
were possible, because, in a moment of sanity, IBM decided to
dedicate some memory at 40:8 et seq. to actually record the base port
addresses of the parallel port adapters one had.
So, rather than compiling the possible port addresses into one's
application, it was only necessary to look at low memory. For
example, if one had a parallel port adapter set for 378h and an MDA
at 3BCh, DOS and the BIOS would normally assign LPT1: to 3BCh and
LPT2: to 378h. However, if an application exchanged the two words at
40:0008 and 40:000A, the reverse mapping would hold.
Cheers,
Chuck
10:26 p.m.
On 4/5/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
Well, you can have as may printer adapters as yopu like if you can set
them all to different addresses and if you're writing your own software
to talk to them...
The way the BIOS looks for printer adapters (and for that matter async
adapters) is quite nice IMHO. The BIOS drivers allow for up to 4 of each
type of adapter, the 'base address' -- the lowest port address used by
each card -- is stored in a parameter table in RAM (I can find the
addresses if you want them). If you store your own values there, you can
have adapters at non-standard addresses, etc.
At boot-up, the BIOS (or is it the POST?) looks for rpinter adapters at
0x3bc (MDA card printer port), 0x378 (primary printer adapter) and 0x278
(secondary printer adapter) in that order. If it finds one, it stores the
base address at the next location in the parameter table. So :
If you have an MDA card, its printer port will always be LPT1: (no matter
what other printer adapters you have).
If you have one printer adapter (wherter on the MDA card, or on a
separate card irrespective as to wheter that card is set to the primary
or secondary address), it'll be LPT1
If you have an MDA card and one printer adapter, then the MDA card will
be LPT1:, the priter adapter will be LPT2: (irrespective of whether the
printer adapter is set to the primary or secondary address).
Much the same applies to async cards, except that the BIOS only looks for
those at 2 addresses (IIRC 30x3f8 (primary) and 0x2f8 (seconmdary))
If youy want 3 or 4 async cards, or 4 printer adapters supported by the
BIOS, yoy have to store the base addresses in the parameter tables yourself.
I am not sure how well documented this is. It's obvious from the BIOS
source listings, but who reads those?
Of coures this doesn't apply to OSes that ignore the BIOS or the
parameter table.
-tony
There are minor differences, mainly due to the
fact that the MDA card's
printer port is at a different address (you can have the MDA card _and_ 2
printer adapters in the same machine).
That's handy to know - every once in a while, I long for a machine
with 2 or 3 parallel adapters, for things like old Connectix cameras,
LCD displays and the like. I've never assembled an ISA machine with
more than one printer adapter. I know that it really doesn't matter
to your own code what the I/O address is, but I wasn't sure how
flexible the underlying hardware might be to being assigned to
alternate addresses.
11:30 p.m.
On 7 Apr 2007 at 22:26, Tony Duell wrote:
I am not sure how well documented this is. It's
obvious from the BIOS
source listings, but who reads those?
Of coures this doesn't apply to OSes that ignore the BIOS or the
parameter table.
I believe the information's also included in the Ralf Brown interrupt
document as well as the (nearly indispensible if you're interested in
BIOS implementations) Phoenix Techref series.
Cheers,
Chuck
8 Apr
8 Apr
12:29 a.m.
On 4/7/07, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
I wrote:
Naturally. The problem I see is that only the older cards might let
you set the printer port to respond to arbitrary addresses - the ones
I have are almost (entirely?) all of the style where you move a single
jumper for LPT1 vs LPT2 (primary vs secondary address).
I wasn't as worried about the OS interpretation since I don't intend
to *print* to my printer port.
-ethan
That's handy to know - every once in a while,
I long for a machine
with 2 or 3 parallel adapters, for things like old Connectix cameras,
LCD displays and the like. I've never assembled an ISA machine with
more than one printer adapter....
Well, you can have as may printer adapters as yopu like if you can set
them all to different addresses and if you're writing your own software
to talk to them...
9:34 p.m.
Well, you can
have as may printer adapters as yopu like if you can set
them all to different addresses and if you're writing your own software
to talk to them...
Naturally. The problem I see is that only the older cards might let
you set the printer port to respond to arbitrary addresses - the ones
6499
days inactive
6502
days old
10 comments
5 participants
participants (5)
-
ard＠p850ug1.demon.co.uk -
cclist＠sydex.com -
ethan.dicks＠gmail.com -
gordon＠gjcp.net -
julesrichardsonuk＠yahoo.co.uk