Datasheet

Input/Output Ports (PORTS)
MC68HC908QB8 Data Sheet, Rev. 3
106 Freescale Semiconductor
12.2.4 Port A Summary Table
The following table summarizes the operation of the port A pins when used as a general-purpose
input/output pins.
12.3 Port B
Port B is an 8-bit special function port that shares its pins with the 4-channel timer interface module (TIM)
(see Chapter 16 Timer Interface Module (TIM)), the 10-bit ADC (see Chapter 3 Analog-to-Digital
Converter (ADC10) Module), the serial peripheral interface (SPI) module (see Chapter 15 Serial
Peripheral Interface (SPI) Module) and the enhanced serial communications interface (ESCI) module
(see Chapter 13 Enhanced Serial Communications Interface (ESCI) Module).
Each port B pin also has a software configurable pullup device if the corresponding port pin is configured
as an input port.
12.3.1 Port B Data Register
The port B data register (PTB) contains a data latch for each of the port B pins.
PTB[7:0] — Port B Data Bits
These read/write bits are software programmable. Data direction of each port B pin is under the control
of the corresponding bit in data direction register B. Reset has no effect on port B data.
Table 12-1. Port A Pin Functions
PTAPUE
Bit
DDRA
Bit
PTA
Bit
I/O Pin
Mode
Accesses to DDRA Accesses to PTA
Read/Write Read Write
10
X
(1)
1. X = don’t care
Input, V
DD
(2)
2. I/O pin pulled to V
DD
by internal pullup.
DDRA5–DDRA0 Pin
PTA5–PTA0
(3)
3. Writing affects data register, but does not affect input.
00X
Input, Hi-Z
(4)
4. Hi-Z = high impedance
DDRA5–DDRA0 Pin
PTA5–PTA0
(3)
X 1 X Output DDRA5–DDRA0 PTA5–PTA0
PTA5–PTA0
(5)
5. Output does not apply to PTA2
Bit 76 5 4 3 2 1Bit 0
Read:
PTB7 PTB6 PTB5 PTB4 PTB3 PTB2 PTB1 PTB0
Write:
Reset: Unaffected by reset
Figure 12-5. Port B Data Register (PTB)