UM82C11-C Bidirectional Printer Port Modification ================================================= This is a bidirectional modification for computers using the 82C11 for their parallel ports. Please note that we give no guarantee that it will work or that everything is correct! Proceed at your own risk! (There is only one mistake as far as we know, but everybdy knows how easy it is to make a typo.) NOTE: An asterix (*) in front of a control signal indicates a negative true signal (low = 1). eg. CS=true when high, *CS=true when low. The UM82C11-C is almost a one chip IBM pc printer interface. It includes all the the registers and buffers for a printer port and needs only some address decoding and a LS245 buffer to hook a PC to a printer (plus some wire of course). It comes in two packages - a 40 pin dual in line (DIP) package, and a 44 lead flat pak. The pin numbers referred to below are for the DIP package. There is a pinout for both packages at the end of this article. Pin 19 on this chip is the Printer Data Output Enable (*POE). The printer data buffers drive the printer data bus when this pin is grounded. On my machine, and probably many others, this pin is simply connected to pin 20 (Ground) next to it to permanently enable the printer data bus. This pin needs to be controlled by the D5 output of the printer control word to make the port bidirectional. Unfortunately the printer control word is internal to this chip and we can't simply add a couple of jumpers (as suggested in Steve Ciarcia's article in Byte-Sept/88, pp 304-305,310) On examining the truth table and some timing diagrams in the spec sheets we find that when *CS and DIR are low and A1 is high we can use the rising edge of *IOW to latch the printer control word. After detailed analysis and consideration of our junkbox the following design presented itself. We used a 74LS10 triple 3 input NAND gate as a decoder and a 74LS379 Quad D flip-flop with Clock enable to latch the data. Schematic Diagram ================= 74LS10 74LS379 ------\ (8)DIR --------|1 \ D5(14) /-------tie /-|2 12>0---\ | | | | (40)+5v--\/\/\-+-|13 / | ------------------------ 4k7 | ------/ | | 4 (D0) 5 12 13 | | ------\ | (6) *IOW ---|9 (CP) (D1,D2,D3)| tie ----+-|3 \ | | | \-|4 6>0-\ | /--|1(*CE) | (18)*CS --------|5 / | | ------\ | | 2 (Q0) | ------/ | \-|11 \ | ------------------------ \---|9 8>0--/ | (39) A1 -----------------------|10 / *POE (19) ------/ (40) +5 --(LS10-14, LS379-16) A 0.01uf decoupling capacitor was added (20)GND --(LS10--7, LS370--8) between +5 and GND. (The numbers in paranthesis are the pin numbers on the 82C11.) Wiring Diagram ============== 40 39 40 6 +5 A1 +5 *IOW | /---\ | /-\ /---\ | | | tie | | | | | | | | tie tie | ------------------------|--- | -------------------------------- |14 13 12 11 10 9 | 8| | |16 15 14 13 12 11 10 9| |+5 | | | | | | | | | | | |1 2 3 4 5 6 | 7| | | 1 2 3 4 5 6 7 8| ------------------------|--- | -------------------------------- | tie tie tie | | | | | | | | tie | | | \-/ | \---/ | | | DIR *CS GND *POE D5 GND 18 18 20 19 14 20 (40) +5 --/\/\/--tie (All pins marked tie are pulled up to +5v through 4k7 this resister. (4.7k ohms)) (40) +5 ---||---GND(20) (This capacitor is connected across the supply 10n for decoupling. (.01 uf)) I built this circuit on a small piece of perf board and hot melt glued it on top of the 82C11. The wires were kept as short as possible and tack soldered to the pins of the 82C11. The circuit board trace connecting pin 19 to GND (pin 20) was cut. The printer seems to work fine and the CHECKDDT program reports that my printer port is now bidirectional. I have yet to finish constructing the DDT51 to see if it really is working as it needs to, but I don't see any reason why it shouldn't be. The next challenge is to see if this can be reduced to one IC. A PAL or something similar should be easy to program for this. ------------------------------------------------------- Alternate Schematic Diagram (untried) ===================================== This should do the same thing, and the parts might be more common. ---------- (14) D5 -----------------------------------|2 5|---------*POE (19) | | ------\ ------------- | 74LS74 | (8)DIR -------O|4 \ | 15|O---|3 | (18)*CS -------O|5 >O| | | 1 4 | (39) A1 --------|6 / | 74LS138 | ---------- ------/ | | | | (6)*IOW -----------------|1 | \--+--/\/\/\---+5v /---|2 | 4k7 GND ---+---|3 | ------------- (40) +5 --(LS14-14, LS138-16) (20)GND --(LS14--7, LS138--8) (The numbers in paranthesis are the pin numbers on the 82C11.) ------------------------------------------------------- Data on the 82C11 ================= UM82C11-C pinout ================ This is the 40 pin Dual in Line package. ___________ Crystal in x1 | 1 40| Vdd Power Supply +5v Crystal in x2 | 2 39| A1 System Address 1 Clock out CLK | 3 38| A0 System Address 0 Clock / 10 DCLK | 4 U 37| P0 Printer Data Bus 0 Reset RST | 5 M 36| P1 | I/O Write *IOW | 6 8 35| P2 |-Data to Printer I/O Read *IOR | 7 2 34| P3 | Direction DIR | 8 C 33| P4 | System Data Bus D0 | 9 1 32| P5 | | D1 |10 1 31| P6 | | D2 |11 - 30| P7 Printer Data Bus 7 | D3 |12 C 29| *ERROR Error input from printer | D4 |13 28| SLCT Select input from printer | D5 |14 27| PE Paper end input from printer | D6 |15 26| *ACK Acknowledge input from printer System Data Bus D7 |16 25| BUSY Busy input from Printer Interrupt IRQ |17 24| *STROB Strobe output to Printer Chip Select *CS |18 23| *AUTOFD Printer feeds one line after printng Data output En *POE |19 22| *INIT Initialize printer Ground (0v) Vss |20 21| *SLCT Select Printer ----------- There is also a flat pack 48 pin version of this IC. Pin 1 on the flat pack is *IOW and the pins follow the same sequence around the package with four not connected pins (pins 40-43) between VDD and X1. P0 *SLCT 36 25 ------------------ A0 37| |24 PE | | (4 NC lines | | pins 40-43) | | | | RST 48| |13 D7 ----------------/ 1 12 *IOW D6 The data sheets give the following truth table for the operation of this chip: Input Output Operation: *CS A1 A0 *IOR *IOW DIR 1 x x x x 0 Inactive (x=don't care) 1) 0 0 0 1 0 0 Write Data to Printer 2) 0 0 0 0 1 1 Read data on printer Bus 3) 0 0 1 0 1 1 Read Status from Printer 4) 0 1 0 1 0 0 Write Control word to the printer 5) 0 1 0 0 1 1 Read control word on Printer control bus 0 1 1 0 x x *****Illegal operation***** 0 ---Others--------------- No Action The 82C11 supports 5 commands: (Addresses are for LPT1). 1) Write data to printer (Out &H378,data) The data written to the 82C11 is latched into the output register. *POE enables or disables the data from being driven onto the printer data bus (GND=Enabled). 2) Read data from the printer bus (data = in &h378). The data on the printer data bus is read back to the computer. If *POE is enabled(GND) this will reflect the output data. If *POE is disabled (+5) it will reflect whatever is on the other end of the printer data bus. 3) Read Status from the Printer (data = in &h379). The data reflects the status of the printer status lines. D7 = Inverted version of BUSY signal - When this goes high the printer is ready to accept data. D6 = *ACK - The printer pulls ACKnowledge low to indicate it has received the data and is ready for more. D5 = PE - Paper End - A high indicate the printer is out of paper. D4 = SLCT - SeLeCT -This signal is high when the printer is on-line. D3 = *ERROR - This pin indicates the printer has a problem. D2 = Not used D1 = Not used D0 = Not used 4) Write Control word to the printer (out &h37a,data). Send control signals to the printer. D7 = Not used D6 = Not used D5 = Not used ***(we use this to enable/disable bidirectional)*** D4 = IRQEN - When this pin is high the 82C11 sends an Interrupt request to PC when *ACK is asserted by the printer. D3 = SLCT - ?? D2 = INIT - INITiate printer (reset printer) D1 = *AUTOFD - When low the printer automatically feeds one line after printing. D0 = STROB - This pin is set to a 1 to tell the printer to read the data on the printer data bus. Pins D3, D2 and D0 are inverted between the control word and the output pins that connect to the printer. (eg. A 1 on D0 will be actually sent to the printer as a low on the *STROB pin) 5) Read Control word from the printer (data=in &h37a). Read what control signals have been sent to the printer. Data bits are the same as above. Note that this will not read what has been stored on D5. ---------------------------------------------------------- February 27, 1991 I welcome any constructive criticism. I know that I do not know everything there is to know about the parallel port and I may have made some mistakes. Please let me know so I can fix them. Thank you. David Meed (506) 375-4029 c/o NBBI Victoria, NB E0J 2A0