
Bit 3
BRLE
0
1
Description
P1
3
and P1
2
function as input/output pins.
P1
3
functions as the BREQ input pin. P1
2
functions as the BACK output pin.
(Initial value)
Bits 2 to 0—Reserved:
These bits cannot be modified and are always read as 1.
9.2.3 Pin Functions in Each Mode
Port 1 operates differently in the expanded modes (modes 1, 2, 3, and 4) and the single-chip mode
(mode 7). Table 9-3 explains how the pin functions are selected in the expanded mode. Table 9-4
explains how the pin functions are selected in the single-chip mode.
Table 9-3 Port 1 Pin Functions in Expanded Modes
Pin
P1
7
/ TMO The function depends on output select bits 3 to 0 (OS3 to OS0) of the 8-bit timer
control/status register (TCSR) and on the P1
7
DDR bit as follows:
Selection of Pin Functions
OS3 to OS0
P1
7
DDR
Pin function
All four bits are 0
0
P1
7
input
At least one bit is 1
0
TMO output
1
1
P1
7
output
P1
6
/ IRQ
1
/ The function depends on the IRQ
1
E bit and the trigger enable bit (TRGE)
ADTRG
in the A/D control register (ADCR) as follows:
IRQ
1
E
0
TRGE
0
Pin function
P1
6
input/
ADTRG
output
1
1
0
1
IRQ
1
input
IRQ
1
and
ADTRG
input
input
When used for P1
6
input/output, the input or output function is selected by P1
6
DDR.
P1
5
/ IRQ
0
The function depends on the IRQ
0
E bit and the P1
5
DDR bit as follows:
IRQ
0
E
P1
5
DDR
Pin function
0
1
0
1
0
1
P1
5
input
P1
5
output
IRQ
0
input
147