Elektra CPU User Manual V1.00
Page 48
Base + 8
Read / Write
Digital I/O Port A
Bit
No. 7 6 5 4 3 2 1 0
Name
A7 A6 A5 A4 A3 A2 A1 A0
Base + 9
Read / Write
Digital I/O Port B
Bit
No. 7 6 5 4 3 2 1 0
Name
B7 B6 B5 B4 B3 B2 B1 B0
Base + 10
Read / Write
Digital I/O Port C
Bit
No. 7 6 5 4 3 2 1 0
Name
C7 C6 C5 C4 C3 C2 C1 C0
These 3 registers are used for digital I/O. The direction of each register is controlled by bits in the
register below.
Base + 11
Read / Write
Digital I/O Control Register
Bit
No. 7 6 5 4 3 2 1 0
Name DIOCTR
X X DIRA
DIRCH X DIRB
DIRCL
The bit assignments of this register are designed to be compatible with the 82C55 chip’s control
register.
DIOCTR
Selects counter I/O signals or digital I/O lines C4-C7 on pins 21-24 of J14:
Pin No.
DIOCTR = 1
DIOCTR = 0
Pin direction for DIOCTR = 0
21
C4
Gate
0
Input
22
C5
Gate
1
Input
23
C6
Clk
1
Input
24
C7
Out
0
Output
NOTE:
If DIOCTR = 0, then the pin direction is as shown above. If DIOCTR = 1 then the pin
direction is controlled by DIRCH.
This bit resets to 1.
DIRA
Port A direction. 0 = output, 1 = input
DIRB
Port B direction: 0 = output, 1 = input
DIRCH
Port C bits 7-4 direction: 0 = output, 1 = input
DIRCL
Port C bits 3-0 direction: 0 = output, 1 = input
