APPENDIX FOURTEEN _________________________________________________________



The XL/XE Parallel Bus
The most exciting new feature on the XL computers is probably the
least heralded and the most unused: the parallel expansion bus port
(PBI) on the back of the machines. It provides direct, unbuffered ac-
cess to all of the address, data, and control lines, allowing the use of
high-speed peripherals (fast parallel I/O disk drives, hard disks, and
custom I/O devices). The April 1985 issue of Analog magazine has an
article by Michael Barton on adding additional memory to his 600XL
via the expansion port. Antic ran a special four-part series by Earl
Rice on the bus from January to April 1985. The bus connector looks
like this:

Top                             Pin     Pin     Bottom
Ground                  GND     1       2       External select
Address output          A0      3       4       A1
                        A2      5       6       A3
                        A4      7       8       A5
                        A6      9       10      GND
                        A7      11      12      A8
                        A9      13      14      A10
                        A11     15      16      A12
                        A13     17      18      A14
                        GND     19      20      A15
Data lines              D0      21      22      D1
(Bidirectional)         D2      23      24      D3
                        D4      25      26      D5
                        D6      27      28      D7
                        GND     29      30      GND
Phase 2 clock output            31      32      GND
Reserved                NC      33      34      Reset output
Interrupt request       (IRQ)   35      36      Ready input
                        NC      37      38      External decoder
                                                output
                        NC      39      40      Refresh output
Column address
output                          41      42      GND
Math pack disable
input                           43      44      Row addr strobe
                        GND     45      46      Latch read/write
                                                out
(+5v dc?)               NC      47      48      NC (+5v dc?)
Audio input                     49      50      GND

Looking at the bus from the back, it looks like this: