Motorola MC9S12C Series, User Manual

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Device User Guide — 9S12C128DGV1/D V01.05
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2.3.9 PE6 / MODB / IPIPE1 — Port E I/O Pin 6
PE6 is a general purpose input or output pin. It is used as a MCU operating mode select pin during reset.
The state of this pin is latched to the MODB bit at the rising edge of RESET. This pin is shared with the
instruction queue tracking signal IPIPE1}. This pin is an input with a pull-down device which is only
active when RESET is low. PE[6] is not available in the 48 / 52 pin package versions.
2.3.10 PE5 / MODA / IPIPE0 — Port E I/O Pin 5
PE5 is a general purpose input or output pin. It is used as a MCU operating mode select pin during reset.
The state of this pin is latched to the MODA bit at the rising edge of RESET. This pin is shared with the
instruction queue tracking signal IPIPE0}. This pin is an input with a pull-down device which is only
active when RESET is low. This pin is not available in the 48 / 52 pin package versions.
2.3.11 PE4 / ECLK— Port E I/O Pin [4] / E-Clock Output
ECLK is the output connection for the internal bus clock. It is used to demultiplex the address and data in
expanded modes and is used as a timing reference. ECLK frequency is equal to 1/2 the crystal frequency
out of reset. The ECLK pin is initially configured as ECLK output with stretch in all expanded modes. The
E clock output function depends upon the settings of the NECLK bit in the PEAR register, the IVIS bit in
the MODE register and the ESTR bit in the EBICTL register. All clocks, including the E clock, are halted
when the MCU is in STOP mode. It is possible to configure the MCU to interface to slow external
memory. ECLK can be stretched for such accesses. Reference the MISC register (EXSTR[1:0] bits) for
more information. In normal expanded narrow mode, the E clock is available for use in external select
decode logic or as a constant speed clock for use in the external application system. Alternatively PE4 can
be used as a general purpose input or output pin.
2.3.12 PE3 / LSTRB — Port E I/O Pin [3] / Low-Byte Strobe (LSTRB)
In all modes this pin can be used as a general-purpose I/O and is an input with an active pull-up out of
reset. If the strobe function is required, it should be enabled by setting the LSTRE bit in the PEAR register.
This signal is used in write operations. Therefore external low byte writes will not be possible until this
function is enabled. This pin is also used as TAGLO in Special Expanded modes and is multiplexed with
the LSTRB function. This pin is not available in the 48 / 52 pin package versions.
2.3.13 PE2 / R/W — Port E I/O Pin [2] / Read/Write
In all modes this pin can be used as a general-purpose I/O and is an input with an active pull-up out of
reset. If the read/write function is required it should be enabled by setting the RDWE bit in the PEAR
register. External writes will not be possible until enabled. This pin is not available in the 48 / 52 pin
package versions.