Pinout for SED9421

Tony Duell ard at
Sun Nov 27 15:02:58 CST 2005

> >I think that's the reason for a lot of the Sanders electronics (the 700 
> >had 3 micropeocessors in it -- 2 Z8s and a Z80) - -to handle the 
> >acceleration of the carriage motor and put the dots down at the right
> time.
> The Durango here is patterned after the Sanders in one respect--it uses a
> fine wire dot-matrix printhead to do multipass character formation through
> a film ribbon.  The quality from a 9 wire printhead is very good.  Includes

The Sanders units I have (both of them, 12/7 and 700) actually use a 7 
pin head and get amazing quality from it (some of the fonts take 8 
pases). There's a PROM (on one of the PCBs in the 12/7 and on the back of 
the prinhead itself in the 700) that contains a table of mechanical 
constants for that particular head (!).

The 12/7 electtonics is a lot simpler. Just one Z80 and a couple of 
Z80-DMA chips, one for the data input (mine is the RS232 version), the 
other to send data to the 'pinfire' electronics. From what I rmember, 
that's a set of state machines.

As I mentioned, the 700 has 3 microprocessors in it, communicating by 
shared memory 9 bits wide. No, not 8 bits and parity, a true 9 bits. I am 
told there was a Sanders 900 that used a 9 pin head, you see....

Alas Snaders neve had downloadable fonts. On the 12/7, the fonts are 
stored in EPROMs on intenral PCBs, some osckets take 2708s, some take 
2716s (the TI 3-rail ones...) some take 2732s. And I think there were 
address decoder PROMs that selected how much of the address space was 
allocated to each socket. What this meant was that you got the fonts it 
was ordered with, and any changes later, even if you had the EPROMs with 
the right font in, was a lot of work.

The 780 doesn't support downloadable fonts either [1], but the fonts on 
this are stored in little EPROM cartridges that plug into connectors in 
front of the carriage. Any font cartridge can go into any slot, you were 
supposed to be able to swapt them around.

[1] Although the hardware almost does. There is a Wr/ line on the font 
cartridge connector, a RAM cartridge could have been made. AFAIK there is 
no support for this in the firmware.

A word of warning for anyone working on a 12/7. There is live mains where 
youy least expect it, since the ribbon feed motor and the sheetfeed motor 
are both AC mains ones. This puts mains on the backplane PCB and on the 
connector PCB at the back.

> downloadable fonts, too--some over an inch tall.  The brains are a 5 MHz
> 8085A with a bunch of ROM and RAM ( all separate from the main CPU).  The
> carriage motor is a 48vdc Litton model with hi-res encoder.  I remember
> hearing that the motor cost almost as much as the rest of the printer--it's
> a finger-breaker too.  To get the half-dot vertical offset for multipass
> printing, it uses a geared-down stepper for the paper feed.

The 12/7 is very simple mechancially. The paper feed roller (which is only 
about 5/16" in diameter) is directly pinned to the stepper motor spindle. 
The carriage feed motor (I still think it's a stepper) has the cable drum 
on its spindle, a steel cable pulls the carriage back and forth. The 
ribbon drive motor (which is one of those AC ones with a built-in 
gearbox) directly drives the ribbon spool. Oh, there's a roller the 
ribbon goes round with holes in its flange and a slotted optoswitch to 
detect that the ribbon has moved and how far (!).

The 700 is rather more complicated. It uses the Diablo ribbon cartridge, 
so it keeps some of the gearing to drive it (now driven by a little 
stepper motor in the carriage, since the ribbon usage is programmable 
(!)). Again the carriage feed is what you'd expect, a steel cable on a 
drum. And I think therer are even a few gears in the paper feed (which is 
very much the system from the Diablo 630)

Have you come across the DEC LA100 (or LA210) that 'dip' the head 
mechanically to get the half dot spacing?


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