
Input/Output Ports (PORTS)
MC68HC908GR16 Data Sheet, Rev. 5.0
132
Freescale Semiconductor
When bit DDRDx is a 1, reading address $0003 reads the PTDx data latch. When bit DDRDx is a 0,
reading address $0003 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit.
Table 12-5 summarizes the operation of the port D pins.
12.5.3 Port D Input Pullup Enable Register
The port D input pullup enable register (PTDPUE) contains a software configurable pullup device for each
of the eight port D pins. Each bit is individually configurable and requires that the data direction register,
DDRD, bit be configured as an input. Each pullup is automatically and dynamically disabled when a port
bit’s DDRD is configured for output mode.
PTDPUE7–PTDPUE0 — Port D Input Pullup Enable Bits
These writable bits are software programmable to enable pullup devices on an input port bit.
1 = Corresponding port D pin configured to have internal pullup
0 = Corresponding port D pin has internal pullup disconnected
Table 12-5. Port D Pin Functions
PTDPUE
Bit
DDRD
Bit
PTD
Bit
I/O Pin
Mode
Accesses to DDRD
Accesses to PTD
Read/Write
Read
Write
10
X(1)
1. X = Don’t care
Input, VDD
(2)
2. I/O pin pulled up to VDD by internal pullup device.
DDRD7–DDRD0
Pin
PTD7–PTD0(3)
3. Writing affects data register, but does not affect input.
00
X
Input, Hi-Z(4)
4. Hi-Z = High imp[edance
DDRD7–DDRD0
Pin
PTD7–PTD0(3)
X
1
X
Output
DDRD7–DDRD0
PTD7–PTD0
Address:
$000F
Bit 7
6
54
321
Bit 0
Read:
PTDPUE7 PTDPUE6 PTDPUE5 PTDPUE4 PTDPUE3 PTDPUE2 PTDPUE1 PTDPUE0
Write:
Reset:
00
000
0
Figure 12-16. Port D Input Pullup Enable Register (PTDPUE)