MC68HC908AT32 Datasheet, PDF (326/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

MC68HC08AS20 Emulator Input/Output Ports
DDRE[7:0] — Data Direction Register E Bits
These read/write bits control port E data direction. Reset clears DDRE[7:0], configuring all port E pins
as inputs.
1 = Corresponding port E pin configured as output
0 = Corresponding port E pin configured as input
NOTE
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.
Figure 27-16 shows the port E I/O logic.
READ DDRE ($000C)
WRITE DDRE ($000C)
RESET
WRITE PTE ($0008)
DDREx
PTEx
PTEx
READ PTE ($0008)
Figure 27-16. Port E I/O Circuit
When bit DDREx is a logic 1, reading address $0008 reads the PTEx data latch. When bit DDREx is a
logic 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. Table 27-5 summarizes the operation of the port E pins.
Table 27-5. Port E Pin Functions
DDRE
PTE
Bit
Bit
I/O Pin
Mode
Accesses to
DDRE
Read/Write
0
X
Input, Hi-Z DDRE[7:0]
1
X
Output
DDRE[7:0]
X = don’t care
Hi-Z = high impedance
1. Writing affects data register, but does not affect input.
Accesses to PTE
Read
Pin
PTE[7:0]
Write
PTE[7:0]⁽¹⁾
PTE[7:0]
MC68HC908AT32 Data Sheet, Rev. 3.1
326
Freescale Semiconductor