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Prometheus CPU User Manual V1.44 Page 58
19. DIGITAL I/O OPERATION
Prometheus contains 24 digital I/O lines organized as three 8-bit I/O ports, A, B, and C. The
direction for each port is programmable, and port C is further divided into two 4-bit halves, each
with independent direction. The ports are accessed at registers Base + 8 through Base + 10
respectively, and the direction register is at Base + 11.
Base + 7 6 5 4 3 2 1 0
8 PA7 PA6 PA5 PA4 PA3 PA2 PA1 PA0
9 PB7 PB6 PB5 PB4 PB3 PB2 PB1 PB0
10 PC7 PC6 PC5 PC4 PC3 PC2 PC1 PC0
11 DIOCTR DIRA DIRCH DIRB DIRCL
The digital I/O lines are located at pins 1 through 24 on the I/O header J14 (see page 14). They
are 3.3V and 5V logic compatible. Each output is capable of supplying –8mA in logic 1 state and
+12mA in logic 0 state. See the specifications on page 62 for more detail.
DIRA, DIRB, DIRCH, and DIRCL control the direction of ports A, B, C4-7, and C0-3. A 0 means
output and a 1 means input. All ports power up to input mode and the output registers are cleared
to zero. When a port direction is changed to output, its output register is cleared to zero. When a
port is in output mode, its value can be read back.
DIOCTR is used to control the function of lines C7-C4 on the I/O connector. When DIOCTR=1,
the lines are C7-C4. When DIOCTR=0, these lines are counter/timer lines:
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