     Trend HSR500 (or UDR700) - PC printer port interface
     ----------------------------------------------------
      +5v            +5V
      ---            ---
       |              |
23 >---+    17 >------+
(+5v)       (SpktE)   |
                      |
            10 >------+
            (ChanE)   |
                     --- 0.1uF
                     ---
                      |
21 >---+    16 >------+---W----o 24
(Gnd)  |    (ChanI)   |          (Gnd)
      ---            ---         <Gnd>
      ///            ///

        1 o----------------+
        (Stb)              |
        <Step>             |
                           |          +-----------< 15
        +----------+       o          |           (TransportE)
        |          |   ----------     |
       ---         |   |   S    |     |      |\
       ///         +---|D      Q|-----+------| >o---Or---o 15
             |\        |        |            |/          (Error)
18 >---------| >o------|>       |o            '04f       <Ready>
(Spkt)       |/        |   R    |
              '04a     ----------
                           o   '74b
                           |
                           |   +5v
                           |   ---
                           |    |
                           +----+



                        +----------------< 14
                        |                (Drive L)
                 |\     |    |\
 3 o------R------| >o---+----| >o---------< 13
 (D1)            |/          |/           (Drive R)
 <Direction>      '04b        '04c

                    '157
                 --------------
                 |            |
20 >-------------|0           |
(Ch1)            |           Y|--------Y----o 13
                 |     a      |             (Sel)
19 >-------------|1           |             <Bit0>
(Ch5)            |------------|
                 |            |
 9 >-------------|0           |
(Ch2)            |           Y|--------Gn---o 12
                 |     b      |             (PE)
 6 >-------------|1           |             <Bit1>
(Ch6)            |------------|
                 |            |
 7 >-------------|0           |
(Ch3)            |           Y|--------Bu---o 10
                 |     c      |             (Ack)
22 >-------------|1           |             <Bit2>
(Ch7)            |------------|
                 |            |
 8 >-------------|0           |   |\
(Ch4)            |           Y|---| >o--Pu---o 11
                 |      d     |   |/         (Busy)
24 >-------------|1           |    '04d      <Bit3>
(Ch8)            |            |
                 | S       E  |
                 --------------
                   |       o
                   |       |
 2 o---------------+       |
 (D0)                     ---
 <NybbleSel>              ///

 Note:
 >--- represents pins on the Trend edge connector. Signal names in ()

 o---- represents pins on the D25 plug for the PC printer port.
       IBM signal names in (). PTR interface signals in <>

