Subject:
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About the first 64 cycles
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sun, 5 Apr 1998 09:13:23 GMT
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Original-From:
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Adrian Susianto <adrian@indonesia.#Spamless#crosswinds.net>
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Viewed:
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1046 times
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From adrian's msg I see that setting the config must be done in the first 64
cycles, my question
is how do u do this?? what program will set this chip??could someone plz
explain just the steps we need to take to achive this,
---------
Hi..
I try to answer...
Every instruction has cycles to execute.
For example:
LDAA has 4 cycles in Extended Addressing Mode
LDAA has 2 cycles in Immidiate Addressing Mode
STAA has 4 cycles in Extented Addressing Mode
etc... (look at instruction lists from Motorola pink book)
68HC11 has some special conditions you can change before the first 64 cycles.
It means, you can change the 68HC11 special conditions (ex: CONFIG register) before the total instructions reach 64
cycles from the starting program.
After the first 64 cycles, you can't change those special conditions, even you still make it, the MCU will ignore it (it
has no effect).
And how to do this ?
Just put your instruction at the top list of your program.
Example to change the CONFIG register:
BPROT EQU $1035
ORG $0
LDS #$FF | 3 cycles
LDAA #$00 ;Data for clearing BPROT | 2 cycles
STAA BPROT ;Clear BPROT | 4 cycles
The total cycles to execute the program are 9 cycles. It is still below 64 cycles, so your CONFIG register still can be
cleared.
But if you clear the CONFIG register after 64 cycles (say your program has reach 70 cycles, then you put LDAA #$00 and
STAA BPROT after that), the MCU will have no effect about clearing the CONFIG register.
I hope it helps..
Regards,
Adrian Susianto
mailto:adrian@indonesia.crosswinds.net.id
ICQ : 7725108
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Message has 1 Reply:
 | | Re: About the first 64 cycles
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| Note that the Handyboard runs in 'special test mode' which has as a benefit a lifting of the 64 cycle limit. Specifically you can switch in and out of single chip mode at will, which is essential for driving the LCD display. --Chuck (26 years ago, 5-Apr-98, to lugnet.robotics.handyboard)
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