Keithley PIO-96 Instruction Manual page 32

B-2 I/O Address Map
Address offsets 0-3, 4-7, 8-11, and 12-15 correspond to the four 8255 PPI chips, each of which
has four ports: three I/O ports and one control port. Each of the 8255 chips acts identically and
independently. (For a full description of the many capabilities of the 8255 chip, refer to the data
sheet of Intel or other 8255 chip manufacturer.)
All the operating modes of the 8255 are supported identically on the PIO-96. However, the
majority of users are likely to operate the 8255 in the simple basic input/output mode (also
called Mode 0 operation). Therefore, only Mode 0 is emphasized here. If you wish to operate the
8255 in Mode 1 (strobed input/output) or Mode 2 (bidirectional bus) configurations, refer to the
8255 data sheet.
NOTE On power up or whenever the computer RESET line is asserted, all I/O
ports of the 8255 are initially set as inputs.
Also, a write to the control register at base address +3 (or +7, +11, or
+15) clears all output ports.
The 16 locations in I/O address space are allocated as shown in Table B-1.
Table B-1
I/O address map
Bits Location
0-23 Base address +0
Base address +1
Base address +2
Base address +3
24-47 Base address +4
Base address +5
Base address +6
Base address +7
Base address +8
48-71 Base address +9
Base address +10 8255 PC Port
Base address +11 8255 Control
Base address +12 8255 PA Port
72-95 Base address +13 8255 PB Port
Base address +14 8255 PC Port
Base address +15 8255 Control
Note that the PIO-96 requires a full block of sixteen I/O addresses. For correct operation, other
adapters must not conflict with any I/O address within this range, even if the upper ports of your
PIO-96 will not be used.
Function Type
8255 PA Port Read/Write
8255 PB Port Read/Write
8255 PC Port Read/Write
8255 Control Write Only
8255 PA Port Read/Write
8255 PB Port Read/Write
8255 PC Port Read/Write
8255 Control Write Only
8255 PA Port Read/Write
8255 PB Port Read/Write
Read/Write
Write Only
Read/Write
Read/Write
Read/Write
Write Only
PIO-96 User's Manual