MC68HC05K1 FREESCALE [Freescale Semiconductor, Inc], MC68HC05K1 Datasheet - Page 73

• Manufacturer Part Number: MC68HC05K1
• Description: HCMOS Microcontroller Unit
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

7.4.3 Pulldown Register B
MC68HC05K0 • MC68HC05K1 — Rev. 2.0
NOTE:
Address:
Port B pins have mask-optional pulldown devices that sink
approximately 100 A. 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
If the pulldown mask option is selected, reset initializes all port A and
port B pins as inputs with pulldown devices turned on.
PDIB1 and PDIB0 — Port B Pulldown Inhibit Bits 1 and 0
Bits 7–2 — Not used
To avoid excessive current draw, connect all unused input pins to V
or V
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.
Reset:
Read:
Write:
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.
Bits 7–2 always read as logic 0s.
Freescale Semiconductor, Inc.
SS
For More Information On This Product,
1 = Corresponding port B pin pulldown device turned off
0 = Corresponding port B pin pulldown device turned on
. Or change I/O pins to outputs by writing to DDRB in user
7-7.
$0011
Bit 7
U
Go to: www.freescale.com
Parallel Input/Output (I/O)
Figure 7-7. Pulldown Register B (PDRB)
= Unimplemented
U
6
U
5
U = Unaffected
U
4
U
3
Parallel Input/Output (I/O)
U
2
PDIB1
1
0
Technical Data
PDIB0
Bit 0
Port B
0
DD