XC912BC32CFU8 Motorola Semiconductor Products, XC912BC32CFU8 Datasheet - Page 92

• Manufacturer Part Number: XC912BC32CFU8
• Description: M68HC12B Family Data Sheet
• Manufacturer: Motorola Semiconductor Products

Bus Control and Input/Output (I/O)
6.3.7 Port E Assignment Register
Data Sheet
92
Special single-chip:
Normal single-chip:
Special expanded:
Normal expanded:
Read: Anytime, if register is in the map
Write: Varies from bit to bit, if register is in the map
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.
In special single-chip mode, the E clock is enabled as a timing reference, and the
other bits of port E are configured for general-purpose I/O.
In normal expanded modes, the reset vector is located in external memory. The E
clock may be required for this access but R/W is only needed by the system when
there are external writable resources. Therefore, in normal expanded modes, only
the E clock is configured for its alternate bus control function and the other bits of
port E are configured for general-purpose I/O. If the normal expanded system
needs any other bus-control signals, PEAR would need to be written before any
access that needed the additional signals.
In special expanded modes, IPIPE1, IPIPE0, E, R/W, and LSTRB are configured
as bus-control signals.
In peripheral mode, the PEAR register is not accessible for reads or writes.
Reset states:
Peripheral:
Address: $000A
Read:
Write:
Figure 6-7. Port E Assignment Register (PEAR)
NDBE
Bit 7
1
0
0
0
1
Bus Control and Input/Output (I/O)
= Unimplemented
CGMTE
6
0
0
0
0
1
PIPOE
5
0
1
0
1
0
NECLK
4
1
0
0
0
1
LSTRE
3
0
1
0
1
0
M68HC12B Family — Rev. 8.0
RDWE
2
0
1
0
1
0
1
0
0
0
0
0
0
MOTOROLA
Bit 0
0
0
0
0
0
0