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 7
6
5
4321
Bit 0
Read:
PE7
PE6
PE5
PE4
PE3
PE2
PE1
PE0
Write:
Reset:
Unaffected by reset
Normal narrow expanded:
0
00010
00
All other modes:
0
00000
00
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 7
654321
Bit 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)