
Parallel Input/Output
MC68HC05JJ6/MC68HC05JP6 — Rev. 3.2
General Release Specification
Freescale Semiconductor
Parallel Input/Output
87
NON-DISCLOSURE
AGREEMENT
REQUIRED
7.4.5 PB0, PBI, PB2, and PB3 Logic
The typical I/O logic shown in Figure 7-8 is used for PB0, PB1, PB2, and
PB3 pins of port B. When these port B pins are programmed as an
output, reading the port bit actually reads the value of the data latch and
not the voltage on the pin itself. When these port B pins are programmed
as an input, reading the port bit reads the voltage level on the pin. The
data latch can always be written, regardless of the state of its DDRB bit.
The operations of the PB0:PB3 pins are summarized in Table 7-2.
Figure 7-8. PB0:PB3 Pin I/O Circuit
PORT BDATA
REGISTER
BIT PBx
DATA DIRECTION
REGISTER B
BIT DDRBx
PULLDOWN
REGISTER B
BIT PDIBx
R
PBx
ANALOG SUBSYSTEM,
AND PROGRAMMABLE
TIMER INPUT CAPTURE
READ $0005
WRITE $0001
READ $0001
WRITE $0011
100
A
PULLDOWN
DEVICE
RESET
INTERNAL
D
AT
A
B
U
S
(PINS PB0, PB1, PB2, PB3)
WRITE $0005
PULLDOWN INHIBIT
MASK OPTION
(ENABLE = 0)