Modes of Operation and Pin Descriptions
MC68HC05X4 Rev 1.0
16
Modes of Operation and Pin Descriptions
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MOTOROLA
Bootloader data
format
Serial data byte format is 8 data bits, no parity, one stop bit. The baud
rate for both transmission and reception will be 9600 for a bus frequency
(f
OP
) of 2MHz.
Serial data packet format is:
(count) (byte 0) (byte 1) . . . (byte (count – 2))
Program execution will automatically commence after the last byte is
received.
Port A pins are used as follows:
PA0
Serial receive data (RXD) – 9600 baud at fOP = 2MHz
PA1
Serial transmit data (TXD) – 9600 baud at fOP = 2MHz
PA2
‘High’
Program enters load/execute mode.
‘Low’
Bootloader program runs a simple test routine which
outputs the contents of the user ROM to port B one byte at a time.
PA3
(This bit is read only if PA2 is ‘High’.)
‘High’
Load – bootloader routine waits for a serial byte. The
first byte received is the total byte count (COUNT) for the message. The
serial bytes received are loaded, starting at RAMST + 1. When all the
bytes have been downloaded the program will automatically begin
executing from RAMST + 1. The program will sit in a Wait loop
indefinitely if fewer than ‘COUNT’ bytes are received.
‘Low’
Execute – The program passes control to RAMST +1.
This can be used to allow Port A to be tested (using a user generated
routine) as follows:
Download program into RAM with PA3 = ‘High’, but
ensuring that ‘COUNT’ is greater than the number of bytes to be
transferred. Now, while the MCU is waiting for further bytes to arrive, apply
a reset signal. Whilst holding RESET low, connect port A as required for
testing, then release RESET. The test program in RAM will now test port A.
PA4
‘High’
This indicates normal operation.
‘Low’
This bit is cleared if an overrun error occurs. The device
should be reset if this happens.
4-modes
F
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