mc68hc908gr16 Freescale Semiconductor, Inc, mc68hc908gr16 Datasheet - Page 134

• Manufacturer Part Number: mc68hc908gr16
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Input/Output Ports (PORTS)
12.6.2 Data Direction Register E
Data direction register E (DDRE) determines whether each port E pin is an input or an output. Writing a 1
to a DDRE bit enables the output buffer for the corresponding port E pin; a 0 disables the output buffer.
DDRE5–DDRE0 — Data Direction Register E Bits
Figure 12-19
When bit DDREx is a 1, reading address $0008 reads the PTEx data latch. When bit DDREx is a 0,
reading address $0008 reads the voltage level on the pin. The data latch can always be written,
regardless of the state of its data direction bit.
134
1. X = Don’t care
2. Hi-Z = High impedance
3. Writing affects data register, but does not affect input.
DDRE
These read/write bits control port E data direction. Reset clears DDRE5–DDRE0, configuring all port
E pins as inputs.
Bit
0
1
1 = Corresponding port E pin configured as output
0 = Corresponding port E pin configured as input
shows the port E I/O logic.
PTE
X
Address:
Bit
Avoid glitches on port E pins by writing to the port E data register before
changing data direction register E bits from 0 to 1.
X
(1)
Reset:
Read:
Write:
READ DDRE ($000C)
WRITE DDRE ($000C)
WRITE PTE ($0008)
READ PTE ($0008)
$000C
Bit 7
Input, Hi-Z
0
0
I/O Pin
Output
Mode
Figure 12-18. Data Direction Register E (DDRE)
= Unimplemented
(2)
6
0
0
Table 12-6. Port E Pin Functions
RESET
MC68HC908GR16 Data Sheet, Rev. 5.0
Figure 12-19. Port E I/O Circuit
DDRE5
5
0
Accesses to DDRE
DDRE5–DDRE0
DDRE5–DDRE0
Table 12-6
Read/Write
NOTE
DDRE4
DDREx
PTEx
4
0
summarizes the operation of the port E pins.
DDRE3
3
0
DDRE2
PTE5–PTE0
2
0
Read
Pin
DDRE1
Accesses to PTE
1
0
Freescale Semiconductor
DDRE0
Bit 0
PTEx
0
PTE5–PTE0
PTE5–PTE0
Write
(3)