MC68HC912BL16 Datasheet, PDF (34/128 Pages) Freescale Semiconductor, Inc – 16-Bit Microcontroller

Freescale Semiconductor, Inc.
PORTE — Port E Register
Bit 7
6
5
4
3
2
Single Chip PE7
PE6
PE5
PE4
PE3
PE2
RESET:
–
–
–
–
–
–
Alt. Pin
Function
DBE
MODB or MODA or
IPIPE1 IPIPE0
ECLK
LSTRB or
TAGLO
R/W
$0008
1
Bit 0
PE1
PE0
–
–
IRQ
XIRQ
This register is associated with external bus control signals and interrupt inputs including data bus en-
able (DBE), mode select (MODB/IPIPE1, MODA/IPIPE0), E clock, data size (LSTRB/TAGLO), read/
write (R/W), IRQ, and XIRQ. When the associated pin is not used for one of these specific functions,
the pin can be used as general-purpose I/O. The port E assignment register (PEAR) selects the function
of each pin. DDRE determines the primary direction of each port E pin when configured to be general-
purpose I/O.
Some of these pins have software selectable pull-ups (DBE, LSTRB, R/W, IRQ, and XIRQ). A single
control bit enables the pull-ups for all these pins which are configured as inputs.
This register is not in the map in peripheral mode or expanded modes when the EME bit is set.
Read and write anytime.
DDRE — Port E Data Direction Register
$0009
Bit 7
6
5
4
3
2
1
Bit 0
DDE7 DDE6 DDE5 DDE4 DDE3 DDE2
0
0
RESET:
0
0
0
0
0
0
–
–
This register determines the primary direction for each port E pin configured as general-purpose I/O.
0 = Associated pin is a high-impedance input
1 = Associated pin is an output
PE[1:0] are associated with XIRQ and IRQ and cannot be configured as outputs. These pins can be
read regardless of whether the alternate interrupt functions are enabled.
This register is not in the map in peripheral mode and expanded modes while the EME control bit is set.
Read and write anytime.
PEAR — Port E Assignment Register
$000A
Bit 7
6
5
4
3
2
1
Bit 0
NDBE
0
PIPOE NECLK LSTRE RDWE
0
0
RESET:
0
–
0
0
0
0
–
–
Normal
Expanded
RESET:
0
–
1
0
1
1
–
–
Special
Expanded
RESET:
1
–
0
1
0
0
–
–
Peripheral
RESET:
1
–
0
1
0
0
–
–
Normal
Single Chip
RESET:
0
–
1
0
1
1
–
–
Special
Single Chip
The PEAR register is used to choose between the general-purpose I/O functions and the alternate bus
control functions of port E. When an alternate control function is selected, the associated DDRE bits are
overridden.
The reset condition of this register depends on the mode of operation because bus-control signals are
needed immediately after reset in some modes.
In normal single-chip mode, no external bus control signals are needed so all of port E is configured for
general-purpose I/O.
MC68HC912BL16
34
For More Information On This Product, _{MC68HC912BL16TS/D}
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