APPENDIX FOURTEEN



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The expansion bus is a complex subject--enough for a whole book.
Refer to Rice's articles which cover the bus in greater detail. The XE
continues the parallel bus, but improves it with a clock line and built-
in +/-5v dc current, (Barton, in his article in Analog, says pins 47
and 48 are already 5v dc on the XL bus.)

Changes on the 130XE
On the 130 XE, the parallel bus is called the enhanced cartridge
interface--ECI--basically, a 14-pin extension to the cartridge slot
which allows external devices to connect to the machine's address
and data bus lines and to access the operating system software and
detect the internal state of the computer, It is functionally similar to
and software-compatible with the PBI described above, The pin uses
for the cartridge and the extension are as follows:

Present 30-pin cartridge connector

Top side

Pin     Place   Description
RD4     A       ROM present
GND     B       Ground
A4-A9   C-J     Address lines
A12     K       Address line
D3      L       Data line
D7      M       Data line
A11     N       Address line
A10     P       Address line
R/W     R       Processor read/write line
PH12    S       System clock line

Bottom side

Pin     Place   Description
S4       1      Chip select line--$8000 to $9FFF
                (right slot address on the 800)
A3       2      Address line
A2       3      Address line