Testing Intel386EXTC microcontroller.

Hi, I have a designed a PCB that has a 512Kbits flash with Intel

386EXTC processor. I am trying to test my PCB by hooking up the data and address lines on logic analyzer and writing simple JMP (short) instruction in 386 assembly language. I know that since my UCS is connected to CS of Flash, processor will go to FFF0h address of Flash and execute the instruction present at FFF0h. My Flash contains these simple instructions:

ADD Opcode FFF0 EBh (opcode for short jump that takes 8 bit(here

05h)dispalcement) FFF1 05h FFF2 00h FFF3 00h FFF4 00h FFF5 00h FFF6 EBh FFF7 03h

On logic analyzer, I should see FFF5 after FFF0/FFF1. Instead, all I see is addresses being incremented sequentially with whatever data is present on the different locations ie I see EB,05 etc on data bus but processor is not executing the instructions. I have tried other instructions too, like NOP and HLT but can't seem to make my processor do what it is asked to do. Can some one suggest what the problem may be and how can I fix it? BS8 of processor is tied low. Thanks

learner

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learner
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No, you should see FFF7. The 5 byte offset is added to the addres AFTER the jump+offset instruction.

But as someone else already pointer out: what you see on the bus might not show what the processor is doing. The CPU might read ahead while the code is pipelined.

meindert

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Meindert Sprang

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