MC68HC908GR16 Datasheet, PDF (133/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Input/Output Ports (PORTS)
Port A
NOTE:
Avoid glitches on port A pins by writing to the port A data register before changing
data direction register A bits from 0 to 1.
Figure 12-4 shows the port A I/O logic.
READ DDRA ($0004)
WRITE DDRA ($0004)
RESET
WRITE PTA ($0000)
V_DD
DDRAx
PTAx
PTAPUEx
READ PTA ($0000)
INTERNAL
PULLUP
DEVICE
PTAx
Figure 12-4. Port A I/O Circuit
When bit DDRAx is a logic 1, reading address $0000 reads the PTAx data latch.
When bit DDRAx is a logic 0, reading address $0000 reads the voltage level on the
pin. The data latch can always be written, regardless of the state of its data
direction bit. Table 12-2 summarizes the operation of the port A pins.
Table 12-2. Port A Pin Functions
PTAPUE
Bit
DDRA
Bit
PTA
Bit
I/O Pin
Mode
1
0
X⁽¹⁾
Input, V_DD(2)
0
0
X
Input, Hi-Z⁽⁴⁾
X
1
X
Output
1. X = Don’t care
2. I/O pin pulled up to V_DD by internal pullup device
3. Writing affects data register, but does not affect input.
4. Hi-Z = High impedance
Accesses
to DDRA
Read/Write
DDRA7–DDRA0
DDRA7–DDRA0
DDRA7–DDRA0
Accesses
to PTA
Read
Write
Pin
PTA7–PTA0⁽³⁾
Pin
PTA7–PTA0⁽³⁾
PTA7–PTA0
PTA7–PTA0
12.2.3 Port A Input Pullup Enable Register
The port A input pullup enable register (PTAPUE) contains a software configurable
pullup device for each of the eight port A pins. Each bit is individually configurable
and requires that the data direction register, DDRA, bit be configured as an input.
Each pullup is automatically and dynamically disabled when a port bit’s DDRA is
configured for output mode.
MC68HC908GR16 — Rev. 1.0
MOTOROLA
Input/Output Ports (PORTS)
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Data Sheet
133