MC68HC05K0 Datasheet, PDF (73/154 Pages) Freescale Semiconductor, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Parallel Input/Output (I/O)
Port B
7.4.3 Pulldown Register B
Port B pins have mask-optional pulldown devices that sink
approximately 100 µA. Clearing the PDIB1 and PDIB0 bits in pulldown
register B turns on the port B pulldown devices. Pulldown register B can
turn on a port B pulldown device only when the port B pin is an input. See
Figure 7-7.
If the pulldown mask option is selected, reset initializes all port A and
port B pins as inputs with pulldown devices turned on.
Address: $0011
Bit 7
6
5
4
3
2
1
Read:
Write:
PDIB1
Reset: U
U
U
U
U
U
0
= Unimplemented
U = Unaffected
Figure 7-7. Pulldown Register B (PDRB)
Bit 0
PDIB0
0
PDIB1 and PDIB0 — Port B Pulldown Inhibit Bits 1 and 0
Writing logic 0s to these write-only bits turns on the port B pulldown
devices. Reading pulldown register B returns undefined data. Reset
clears PDIB1 and PDIB0.
1 = Corresponding port B pin pulldown device turned off
0 = Corresponding port B pin pulldown device turned on
Bits 7–2 — Not used
Bits 7–2 always read as logic 0s.
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 DDRB in user
initialization code. Avoid a floating port B input by clearing its pulldown
register bit before changing its DDRB bit from logic 1 to logic 0.
Because pulldown register B is a write-only register, using the
read-modify-write instruction may result in inadvertently turning bits on
or off.
MC68HC05K0 • MC68HC05K1 — Rev. 2.0
Parallel Input/Output (I/O)
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Technical Data