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| MC68HC05B6_13 Datasheet, PDF (228/302 Pages) Freescale Semiconductor, Inc – Microcontrollers | |||
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F.5
Bootstrap mode
Oscillator divide-by-two is forced in bootstrap mode.
The 432 bytes of self-check firmware on the MC68HC05B6 are replaced by 576 bytes of bootstrap
firmware. 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 âhighâ 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 firmware will start to execute. Table F-4 shows the conditions required
to enter each level of bootstrap mode on the rising edge of RESET.
Table F-4 Mode of operation selection
IRQ pin
VSS to VDD
2xVDD
2xVDD
2xVDD
TCAP1 pin
VSS to VDD
VDD
VDD
VDD
2xVDD
VDD
2xVDD
VDD
2xVDD
VDD
x = Donât care
PD1 PD2 PD3 PD4
Mode
x x x x Single chip
0 0 0 0 Erased EPROM verification
0 0 1 0 EPROM verification;
1
0
0
0
EPROM verification; erase EEPROM;
EPROM/EEPROM parallel program/verify
1
0
1
0
Erased EPROM verification; erase EEPROM;
EPROM parallel program/verify (no E2)
1 0 0 1 Jump to start of RAM ($0051); SEC bit = NON ACTIVE
x
0
1
1
Serial RAM load/execute â similar to MC68HC05B6 but can fill RAM I
and II
The bootstrap program will first copy part of itself in RAM (except âRAM parallel loadâ), as the
program cannot be executed in ROM during verification/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.
14
Freescale
F-10
MC68HC705B16N
MC68HC05B6
Rev. 4.1
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