Mitsubishi Electronics FX1S manual Binary Coded Decimal value= Error, Word Data Summary

FX Series Programmable Controllers Devices in Detail 4

c)ABCD conversion

Using the original bit pattern as a base but adding the following BCD headers allows the conversion of the binary data into a BCD format.

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8 4 2 1 8 4 2 1 8 4 2 1 8 4 2 1

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Binary Coded Decimal value= ERROR!!!!!

It will be noticed that this will produce an ERROR. The conversion will not be correct. This is because BCD numbers can only have values from 0 to 9, but the second block of 4 bit devices from the left would have a value of 14. Hence, the error.

The conversion process is very similar to that of hexadecimal except for the mentioned limit on values of 0 to 9. If the other blocks were converted just as an example the following values would be found;

Extreme Left Hand Block= ((1 × 8) + (1 × 1)) = 9

Second Right Hand Block= ((1 × 4) + (1 × 2) + (1 × 1)) = 7

Extreme Right Hand Block= ((1 × 4) + (1 × 1)) = 5

BCD data is read from left to right as a normal number would be read. Therefore, in this example the “9” would actually represent “9000”. The second right hand block is actually “70” not “7”. The units are provided by the extreme right hand block, i.e. 5. The hundreds “100’s” would have been provided by the second left hand block (which is in error).

It is also important to note that there is no sign with BCD converted data. The maximum number allowable for a single data word is “9999” and the minimum is “0000”.

Word Data Summary

In each of the previous cases the original bit pattern had a further meaning. To recap the three new readings and the original bit pattern,

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Decimal	:	-24971
Hexadecimal	:	9E75
BCD	:	Error (9?75)

Each meaning is radically different from the next yet they are all different ways of describing the same thing. They are in fact all equal to each other!

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