MC68HC11PH8 Datasheet, PDF (48/264 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

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PH8.DS03/Modes+mem
stretches externally, but the internal clocks are not affected so that timers and serial systems are not
corrupted. See Section 3.3.2.5.
EEPROM data can be protected while in expanded mode, using a security feature described in
Section 3.4.4.
3.1.3 Special test -mode
Special test, a variation of the expanded mode, is primarily used during Motorola’s internal
production testing; however, it is accessible for programming the CONFIG register, programming
calibration data into EEPROM, and supporting emulation and debugging during development.
3.1.4 Special bootstrap mode
When the MCU is reset in special bootstrap mode, a small on-chip ROM is enabled at address
$BE40–$BFFF. The ROM contains a reset vector and a bootloader program. The MCU fetches the
reset vector, then executes the bootloader.
For normal use of the bootloader program, send a synchronization byte $FF to the SCI receiver
at either E clock ÷256, or E clock ÷1664 (7812 or 1200 baud respectively, for an E clock of 2MHz).
Then download up to 2048 bytes of program data (which is put into RAM starting at $0080). These
characters are echoed through the transmitter. The bootloader program ends the download after
a timeout of four character times or 2048 bytes. When loading is complete, the program jumps to
location $0080 and begins executing the code. Use of an external pull-up resistor is required when
using the SCI transmitter pin (TXD) because port D pins are configured for wired-OR operation by
the bootloader. In bootstrap mode, the interrupt vectors point to RAM. This allows the use of
interrupts through a jump table.
Further baud rate options are available on the MC68HC11PH8 by using a different value for the
synchronization byte, as shown in the Table 3-1.
A special mode exists that allows a low frequency crystal to be used if the PLL is active. In this case,
the value on port F is loaded into the SYNR register just after reset, to be used as the multiplication
factor for the crystal frequency. If the PLL is not active, then the bootloader runs at the crystal
frequency. Refer to Section 2.5 for more information on the operation of the PLL circuitry.
Refer also to Motorola application note AN1060, M68HC11 Bootstrap Mode (the bootloader
mode is similar to that used on the MC68HC11K4).
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MOTOROLA
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OPERATING MODES AND ON-CHIP MEMORY
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MC68HC11PH8