MC68HC05K0 Datasheet, PDF (68/154 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Technical Data
Freescale Semiconductor, Inc.
7.3.3 Pulldown Register A
Port A pins have mask-optional pulldown devices that sink
approximately 100 µA. Clearing the PDIA7–PDIA0 bits in pulldown
register A turns on the port A pulldown devices. Pulldown register A,
shown in Figure 7-3, can turn on a port A pulldown device only when the
port A pin is an input.
If the pulldown mask option is selected, reset initializes all port A and port
B pins as inputs with pulldown devices turned on.
Address: $0010
Bit 7
6
5
4
3
2
1
Read:
Write: PDIA7 PDIA6 PDIA5 PDIA4 PDIA3 PDIA2 PDIA1
Reset: 0
0
0
0
0
0
0
= Unimplemented
Figure 7-3. Pulldown Register A (PDRA)
Bit 0
PDIA0
0
PDIA7–PDIA0 — Port A Pulldown Inhibit Bits 7–0
Writing logic 0s to these write-only bits turns on the port A pulldown
devices. Reading pulldown register A returns undefined data. Reset
clears bits PDIA7–PDIA0.
1 = Corresponding port A pin pulldown device turned off
0 = Corresponding port A pin pulldown device turned on
NOTE:
To avoid excessive current draw, connect all unused input pins to V_DD
or V_SS. Or change I/O pins to outputs by writing to DDRA in user
initialization code. Avoid a floating port A input by clearing its pulldown
register bit before changing its DDRA bit from logic 1 to logic 0.
Because pulldown register A is a write-only register, using the
read-modify-write instruction may result in inadvertently turning bits on
or off.
Technical Data
MC68HC05K0 • MC68HC05K1 — Rev. 2.0
Parallel Input/Output (I/O)
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