MOTOROLA
F-10
MC68HC05B6
Rev. 4
MC68HC705B16N
14
F.5
Bootstrap mode
Oscillator divide-by-two is forced in bootstrap mode.
The 432 bytes of self-check rmware on the MC68HC05B6 are replaced by 576 bytes of bootstrap
rmware. A detailed description of the modes of operation within bootstrap mode is given below.
The bootstrap program in mask ROM address locations $0200 to $024F and $3E00 to $3FEF can
be used to program the EPROM and the EEPROM, to check if the EPROM is erased or to load
and execute data in RAM.
After reset, while going to the bootstrap mode, the vector located at address $3FEE and $3FEF
(RESET) is fetched to start execution of the bootstrap program. To place the part in bootstrap
mode, the IRQ pin should be at 2xVDD with the TCAP1 pin ‘high’ during transition of the RESET
pin from low to high. The hold time on the IRQ and TCAP1 pins is two clock cycles after the external
RESET pin is brought high.
When the MC68HC705B16N is placed in the bootstrap mode, the bootstrap reset vector will be
fetched and the bootstrap rmware will start to execute.
Table F-4 shows the conditions required
to enter each level of bootstrap mode on the rising edge of RESET.
The bootstrap program will rst copy part of itself in RAM (except ‘RAM parallel load’), as the
program cannot be executed in ROM during verication/programming of the EPROM. It will then
set the TCMP1 output to a logic high level, unlike the MC68HC05B6 which keeps TCMP1 low. This
can be used to distinguish between the two circuits and, in particular, for selection of the VPP level
and current capability.
Table F-4 Mode of operation selection
IRQ pin
TCAP1 pin PD1 PD2 PD3 PD4
Mode
VSS to VDD
xxxx
Single chip
2xVDD
VDD
0000
Erased EPROM verication
2xVDD
VDD
0010
EPROM verication;
2xVDD
VDD
1000
EPROM verication; erase EEPROM;
EPROM/EEPROM parallel program/verify
2xVDD
VDD
1010
Erased EPROM verication; erase EEPROM;
EPROM parallel program/verify (no E2)
2xVDD
VDD
1001
Jump to start of RAM ($0051); SEC bit = NON ACTIVE
2xVDD
VDD
x
011
Serial RAM load/execute – similar to MC68HC05B6 but can ll RAM I
and II
x = Don’t care
TPG
222
05B6Book Page 10 Tuesday, April 6, 1999 8:24 am