MC68HC05B4 Datasheet, PDF (175/298 Pages) Motorola, Inc – High-density Complementary Metal Oxide Semiconductor (HCMOS) Microcomputer Unit

C.5.3 EPROM (RAM) serial bootstrap load and execute
The serial routine communicates through the SCI with an external host, typically a PC, by means
of an RS232 link at 9600 baud, 8-bit, no parity and full duplex.
Data format is not ASCII, but 8-bit binary, so a complementary program must be run by the host to
supply the required format. Such a program is available for the IBM PC from Motorola.
The EPROM bootstrap routines are used to customise the OTP EPROM. To increase the speed
of programming, four bytes are programmed in parallel while the data is simultaneously
transmitted and received in full duplex. This implies that while 4 bytes are being programmed, the
next 4 bytes are received and the preceding 4 bytes are echoed. The format accepted by the serial
loader is as follows:
[address n high] [address n low] [data(n)] [data (n+1)] [data (n+2)] [data (n+3)]
Address n must have the two LSBs at zero so that n, n+1, n+2 and n+3 have identical MSBs. These
blocks of four bytes do not need to be contiguous, as a new address is transmitted for each new
group.
The protocol is as follows:
1 The MC68HC705B5 sends the last two bytes programmed to the host as a
prompt; this allows verification by the host of proper programming.
1) In response to the first byte prompt, the host sends the first address byte.
2) After receiving the first address byte, the MC68HC705B5 sends the next
byte programmed.
3) The exchange of data continues until the MC68HC705B5 has sent the four
data bytes and the host has sent the 2 address data bytes and 4 data bytes.
4) If the data is non zero, it is programmed at the address provided, while the
next address and bytes are received and the previous data is echoed.
5) Loop to 1.
After reset, the MC68HC705B5 serial bootstrap routine will first echo two blocks of four bytes at
$0000, as no data is programmed yet.
If the data sent in is $00, no programming in the EPROM takes place, and the contents of the
accessed location are returned as a prompt. The entire EPROM memory can be read in this
fashion (serial dump). The red LED will be on if the data read from the EPROM is not $00.
Serial RAM loading and execute can be accomplished in this mode. A RAM byte will be written if
the address sent by the host in the serial protocol points to the RAM.
In the RAM bootloader mode, all interrupt vectors are mapped to pseudo-vectors in RAM (see
Table C-3). 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.
14
MC68HC05B6
Rev. 4
MC68HC705B5
TPG
MOTOROLA
C-13