Pinout for SED9421

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. 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? -tony