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                           Parallel Printer Port

      Port 3BC printer data output  (readable)

         |7|6|5|4|3|2|1|0|  ports 278, 378, 3BC
          | | | | | | | +---- data bit 0, hardware pin 2
          | | | | | | +----- data bit 1, hardware pin 3
          | | | | | +------ data bit 2, hardware pin 4
          | | | | +------- data bit 3, hardware pin 5
          | | | +-------- data bit 4, hardware pin 6
          | | +--------- data bit 5, hardware pin 7
          | +---------- data bit 6, hardware pin 8
          +----------- data bit 7, hardware pin 9

      Port 3BD printer status register   (Parallel Printer Port)

         |7|6|5|4|3|2|1|0|  ports 279, 379, 3BD
          | | | | | | | +---- 1 = time-out
          | | | | | +------- unused
          | | | | +-------- 1 = error,  pin 15
          | | | +--------- 1 = on-line,  pin 13
          | | +---------- 1 = out of paper,  pin 12
          | +----------- 0 = Acknowledge,  pin 10
          +------------ 0 = busy,  pin 11

      Port 3BE printer control register   (Parallel Printer Port)

         |7|6|5|4|3|2|1|0|  ports 27A, 37A, 3BE
          | | | | | | | +---- 1 = output data to printer,  (pin 1)
          | | | | | | +----- 1 = auto line feed,  (pin 14)
          | | | | | +------ 0 = initialize printer,  (pin 16)
          | | | | +------- 1 = printer reads output,  (pin 17)
          | | | +-------- 0 = IRQ disable,1=IRQ enable for ACK
          +------------- unused