MC68HC05L28 Datasheet, PDF (138/156 Pages) Motorola, Inc – Flexible general-purpose microcomputer

A.2.3 RAM bootloader mode
In addition to the EPROM bootloader mode on the MC68HC705L28, there is a RAM bootloader
mode that allows the user to perform simple load and execute instructions in ROM. To make use
of this feature a circuit board should be constructed as shown in Figure A-1.
In the RAM bootloader mode all interrupt vectors are mapped to pseudo-vectors in RAM (see
Table A-2). 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 user’s service
routine address.
Table A-2 MC68HC705L28 bootloader mode jump vectors
Address Pseudo-vector
0083 Software interrupt
0086 IRQ
0089 Core timer
008C I²C-bus
008F 16 bit timer
A.3
VPP
The VPP pin is the voltage input for the EPROM in both read and programming modes.
15
MOTOROLA
A-4
MC68HC705L28
TPG
MC68HC05L28