Keithley PIO-12 User Manual page 57

A power-up or reset automatically configures all ports as inputs. This
configuration remains intact until changed by a write to the control
register. The initialization section of your program should set the port
configuration. Table C-2 illustrates how the port configuration is derived
from the control word.
Table C-2. Derivation of Port Configuration from Control Word
Bit # Setting
7
6 and 5
4
3
2
1
0
Bit
Configuration
0 Bit set/reset mode for PC0 to PC7
1 Mode set active for PC0 to PC7
00 Mode 0 for PA4 to PA7 and PC4 to PC7
01 Mode 1 for PA4 to PA7 and PC4 to PC7
10 Mode 2 for PA4 to PA7 and PC4 to PC7
1X Mode 2 for PA4 to PA7 and PC4 to PC7
0 PA output
1 PA input
0 PC4 to PC7 output
1 PC4 to PC7 input
0 PB0 to PB3 and PC0 to PC3 output
1 PB0 to PB3 and PC0 to PC3 input
0 PB output
1 PB input
0 PC0 to PC3 output
1 PC0 to PC3 input
C-3