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发表于 2015-2-28 16:09:06
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Sorry if I have misunderstood. I'm afraid I do not speak Chinese.
Let me give some more information in case it is useful. If it isn't please ignore.
Two copies of R6551 calibration data is stored in TC5564 at 0x7413-0x755C and 0x7567-0x76B0.
The first byte of each block 0x7413 and 0x7567 are checksums. On power up, both checksums are verified and if both are incorrect then ERR CA is displayed and the machine freezes.
When you apply power to the TC5564 it will contain random data. Each checksum will be correct 1 time in 256. So about 1 in 100 times one checksum will be correct and ERR CA will not be displayed. But the calibration data is still random. Because of this the R6551 will probably display OL and not allow calibration, even if there is no hardware error.
If you power up with CAL switch in and V DC and SHIFT pressed then both blocks of calibration data are copied from the 27C256 ROM, and the meter can now make readings and be calibrated.
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