Bus Control and Input/Output (I/O)
MC68HC812A4 Data Sheet, Rev. 7
70
Freescale Semiconductor
PIPOE — Pipe Status Signal Output Enable Bit
Normal modes: Write once
Special modes: Write anytime except the first time
1 = PE6 and PE5 are outputs and indicate the state of the instruction queue; no effect in single-chip
modes.
0 = PE6 and PE5 are general-purpose I/O; if PLLTE = 1, PE6 is a test output signal from the PLL
module.
NECLK — No External E Clock Bit
Normal modes: Write anytime
Special modes: Write never
In peripheral mode, E is an input; in all other modes, E is an output.
1 = PE4 is a general-purpose I/O pin.
0 = PE4 is the external E-clock pin. To get a free-running E-clock in single-chip modes, use
NECLK = 0 and IVIS = 1. A 16-bit write to PEAR:MODE can configure these bits in one
operation.
LSTRE — Low Strobe (LSTRB) Enable Bit
Normal modes: Write once
Special modes: Write anytime except the first time
LSTRE has no effect in single-chip or normal expanded narrow modes.
1 = PE3 is configured as the LSTRB bus-control output, except in single-chip or normal expanded
narrow modes.
0 = PE3 is a general-purpose I/O pin.
LSTRB is for external writes. After reset in normal expanded mode, LSTRB is disabled. If needed, it
must be enabled before external writes. External reads do not normally need LSTRB because all 16
data bits can be driven even if the MCU only needs eight bits of data.
In normal expanded narrow mode, this pin is reset to an output driving high allowing the pin to be an
output while in and immediately after reset.
RDWE — Read/Write Enable Bit
Normal modes: Write once
Special modes: Write anytime except the first time
RDWE has no effect in single-chip modes.
1 = PE2 is configured as the R/W pin. In single-chip modes, RDWE has no effect and PE2 is a
general-purpose I/O pin.
0 = PE2 is a general-purpose I/O pin.
R/W is used for external writes. After reset in normal expanded mode, it is disabled. If needed, it must
be enabled before any external writes.