MC68HC05B4 Datasheet, PDF (232/298 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

F.5.3 Serial RAM loader
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 F-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. 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 and
II. 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 F-5). This allows programmers to use their own service-routine addresses. Each
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 F-5 Bootstrap vector targets in RAM
Vector targets in RAM
SCI interrupt
Timer overflow
Timer output compare
Timer input capture
IRQ
SWI
$0063
$0060
$005D
$005A
$0057
$0054
F.5.3.1 Jump to start of RAM ($0051)
The Jump to start of RAM program will be executed when the device is brought out of reset with
PD1 and PD4 at ‘1’ and PD2 and PD3 at ‘0’.
14
MOTOROLA
F-16
MC68HC705B16N
TPG
MC68HC05B6
Rev. 4