Datasheet
Bus Control and Input/Output (I/O)
MC68HC812A4 Data Sheet, Rev. 7
68 Freescale Semiconductor
6.3.9 Port E Data Register
Read: Anytime, if register is in the map
Write: Anytime, if register is in the map
This register is associated with external bus control signals and interrupt inputs including auxiliary reset
(ARST), mode select (MODB/IPIPE1, MODA/IPIPE0), E-clock, size (LSTRB
), 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 pullups (LSTRB
, R/W, and XIRQ). A single control bit
enables the pullups for all these pins which are configured as inputs. IRQ
always has a pullup.
PE7 can be selected as a high-true auxiliary reset input.
This register is not in the map in peripheral mode or expanded modes when the EME bit is set.
6.3.10 Port E Data Direction Register
Read: Anytime, if register is in the map
Write: Anytime, if register is in the map
This register determines the primary direction for each port E pin configured as general-purpose I/O.
1 = Associated pin is an output.
0 = Associated pin is a high-impedance input.
PE1 and PE0 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.
Address: $0008
Bit 7654321Bit 0
Read:
PE7 PE6 PE5 PE4 PE3 PE2 PE1 PE0
Write:
Reset: Unaffected by reset
Normal narrow expanded:00001000
All other modes:00000000
Alternate pin function: ARST
MODB or
IPIPE1
MODA or
IPIPE0
ECLK LSTRB R/W
IRQ XIRQ
Figure 6-9. Port E Data Register (PORTE)
Address: $0009
Bit 7654321Bit 0
Read:
DDRE7 DDRE6 DDRE5 DDRE4 DDRE3 DDRE2 DDRE1 DDRE0
Write:
Reset:00000011
Normal narrow expanded: 00001000
All other modes:00000000
Figure 6-10. Port E Data Direction Register (DDRE)