MC68HC908GT16_07 Datasheet, PDF (127/292 Pages) Freescale Semiconductor, Inc – Microcontrollers

Figure 12-4 shows the port A I/O logic.
READ DDRA ($0004)
WRITE DDRA ($0004)
RESET
WRITE PTA ($0000)
DDRAx
PTAx
Port A
V_DD
PTAPUEx
45 k
PTAx
READ PTA ($0000)
Figure 12-4. Port A I/O Circuit
When bit DDRAx is a 1, reading address $0000 reads the PTAx data latch. When bit DDRAx is a 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
Pin
Pin
Write
PTA7–PTA0⁽³⁾
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
.
Address: $0004
Bit 7
6
5
4
3
2
1
Bit 0
Read:
PTAPUE7 PTAPUE6 PTAPUE5 PTAPUE4 PTAPUE3 PTAPUE2 PTAPUE1 PTAPUE0
Write:
Reset: 0
0
0
0
0
0
0
0
Figure 12-5. Port A Input Pullup Enable Register (PTAPUE)
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
127