2. Port 3 Data Register (P3DR)—H'FF86
P3DR is an 8-bit register containing the data for pins P37 to P30.
At a reset and in the hardware standby mode, P3DR is initialized to H'00.
When the CPU reads P3DR, for output pins it reads the value in the P3DR latch, but for input
pins, it obtains the pin status directly.
9.4.3 Pin Functions in Each Mode
Port 3 has different functions in the expanded modes (modes 1, 2, 3, 4) and the single-chip mode
(mode 7). Separate descriptions are given below.
Pin Functions in Expanded Modes: In the expanded modes (modes 1, 2, 3, and 4), port 3 is
automatically used as the data bus and P3DDR is ignored. Figure 9-6 shows the pin functions
for the expanded modes.
Bit 76543210
P3
7 P36 P35 P34 P33 P32 P31 P30
Initial value 00000000
Read/Write R/W R/W R/W R/W R/W R/W R/W R/W
D7 (input/output)
D
6 (input/output)
D
5 (input/output)
Port D
4 (input/output)
3D
3 (input/output)
D
2 (input/output)
D
1 (input/output)
D
0 (input/output)
Figure 9-6 Port 3 Pin Functions in Expanded Modes
153
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