MC68HC05B4 Datasheet, PDF (265/298 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

H.5.3 Serial RAM loader
Preliminary ^{This mode is similar to the RAM load/execute program for the MC68HC05B6 described in}
Section 2.2, with the additional features listed below. Table H-4 shows the entry conditions
required for this mode.
If the first byte is less than $B0, the bootloader behaves exactly as the MC68HC05B6, i.e. count
byte followed by data stored in $0050 to $00FF. If the count byte is larger than RAM I (176 bytes)
then the code continues to fill RAM II then RAM III. In this case the count byte is ignored and the
program execution begins at $0051 once the total RAM area is filled or if no data is received for 5
milliseconds.
The user must take care when using branches or jumps as his code will be relocated in RAM I, II
and III. If the user intends to use the stack in his program, he should send NOP’s to fill the desired
stack area.
In the RAM bootloader mode, all interrupt vectors are mapped to pseudo-vectors in RAM (see
Table H-5). This allows programmers to use their own service-routine addresses. Each
Preliminary ^{pseudo-vector is allowed three bytes of space rather than the two bytes for normal vectors,}
because an explicit jump (JMP) opcode is needed to cause the desired jump to the users
service-routine address.
Table H-5 Bootstrap vector targets in RAM
Vector targets in RAM
SCI interrupt
Timer overflow
Timer output compare
Timer input capture
$0063
$0060
$005D
$005A
IRQ
$0057
SWI
$0054
Preliminary ^{H.5.3.1 Jump to start of RAM ($0051)}
The Jump to start of RAM program will be executed when bring the device out of reset with PD2
and PD3 at ‘1’ and PD4 at ‘0’.
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MC68HC05B6
Rev. 4
MC68HC705B32
TPG
MOTOROLA
H-19