Motherboard I/O Port Addressing - NorthStar HORIZON Manual

MOTHERBOARD I/O PORT ADDRESSING
A block of eight contiguous I/O ports is specified by
configuration of the Port Select header at location 5B. The 14-
pin header is configured to specify the Eive bit value which
matches address bits A3-A? during an IN or OUT instruction, as
follows:
address bit
7
header pln
9
address bit
6
header pln 10
address bit 5
header pln 11
address bit 4 header pln 12
address bit 3 header pin 13
Each address bit that should match a "one" should be connected to
pin 1 of the header and each address bit that should match a
"zero" should be connected to pin 7. For example, if ports AR-AF
are desired, then A3-A? should be "10101". 'rhus, pin 7 should be
connected to pins 10 and 12 and pin 1 should be connected to pins
9, 11 and 13.
Within a block of eight I/O ports, address bits A0-A2 are decoded
as follows:
71
A0-A2
o
1
2
3
4
5
6
?
Function
Parallel I/O Data
(same as 0)
Standard Serial I/O Data
Standard Serial I/O Control
Second Serial I/O Data
Second Serial I/O Control
Motherboard Control and Status
(same as 6)
North Star HORIZON Computer