MC9S12E Motorola, MC9S12E Datasheet - Page 83

• Manufacturer Part Number: MC9S12E
• Description: MC9S12E-Family Device User Guide V01.04
• Manufacturer: Motorola

Freescale Semiconductor, Inc.
Device User Guide — 9S12E128DGV1/D V01.04
instruction queue tracking signal IPIPE1. This pin is an input with a pull-down device which is only active
when RESET is low. PE6 is not available in the 80 pin package version.
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. PE5 is not available in the 80 pin package version.
2.3.11 PE4 / ECLK— Port E I/O Pin 4 / E-Clock Output
PE4 is a general purpose input or output pin. In Normal Single Chip mode PE4 is configured with an active
pull-up while in reset and immediately out of reset. The pullup can be turned off by clearing PUPEE in the
PUCR register. In all modes except Normal Single Chip Mode, the PE4 pin is initially configured as the
output connection for the internal bus clock(ECLK). ECLK is used as a timing reference and to
demultiplex the address and data in expanded modes. The ECLK frequency is equal to 1/2 the crystal
frequency out of reset. The ECLK 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 ECLK, 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. The PE4 pin is initially
configured as ECLK output with stretch in all expanded modes. Reference the MISC register
(EXSTR[1:0] bits) for more information. In normal expanded narrow mode, the ECLK is available for use
in external select decode logic or as a constant speed clock for use in the external application system.
2.3.12 PE3 / LSTRB / TAGLO — Port E I/O Pin 3 / Low-Byte Strobe (LSTRB)
PE3 can be used as a general-purpose I/O in all modes and is an input with an active pull-up out of reset.
The pullup can be turned off by clearing PUPEE in the PUCR register. PE3 can also be configured as a
Low-Byte Strobe (LSTRB). The LSTRB signal is used in write operations, so external low byte writes will
not be possible until this function is enabled. LSTRB can be enabled by setting the LSTRE bit in the PEAR
register. In Expanded Wide and Emulation Narrow modes, and when BDM tagging is enabled, the LSTRB
function is multiplexed with the TAGLO function. When enabled a logic zero on the TAGLO pin at the
falling edge of ECLK will tag the low byte of an instruction word being read into the instruction queue.
PE3 is not available in the 80 pin package version.
2.3.13 PE2 / R/W — Port E I/O Pin 2 / Read/Write
PE2 can be used as a general-purpose I/O in all modes and is configured an input with an active pull-up
out of reset. The pullup can be turned off by clearing PUPEE in the PUCR register. 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 the read/write function is enabled. The PE2 pin is not available in the 80 pin
package version.
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