2 byte result

Farmer Scott

I think I know the answer to this one, but was hoping someone could help me and verify...

I want to send a two byte I2C result as a return code from a public function, using the Basic I2C Driver from the object exchange...

Is this valid to assign both bytes to result:

Result[noparse][[/noparse]0] := I2C.Read(SCL, NAK)
Result[noparse][[/noparse]1] := I2C.Read(SCL, ACK)

Thanks in advance...

Scott

Paul Baker

You are close but not quite right, indirect data (which arrays are an example of) is accessed via BYTE, WORD, or LONG. So for your example, say you have declared Result as type WORD, to access the least significant byte you would use BYTE[noparse][[/noparse]@Result][noparse][[/noparse]0] (the second bracket in this example is optional, but for symmetry when accessing multiple elements·you should include it). To access the most significant byte you use BYTE[noparse][[/noparse]@Result][noparse][[/noparse]1]. Which one goes first depends on the endian-ness of the device you're interfacing with. If it's little endian you assign to BYTE[noparse][[/noparse]@Result][noparse][[/noparse]0] then BYTE[noparse][[/noparse]@Result][noparse][[/noparse]1]. If it's big endian you assign to BYTE[noparse][[/noparse]@Result][noparse][[/noparse]1] then BYTE[noparse][[/noparse]@Result][noparse][[/noparse]0].

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Ariba

Another solution:
result := I2C.Read(SCL, NAK) + I2C.Read(SCL, ACK)<<8

'result' is always a long, so you can pack up to 4 bytes in it. Here the first byte is in bits7..0 and the scond in bits 15..8.
To separate theme again:
first := result & 255
second := result >> 8

Andy

Farmer Scott

Paul & Andy,

Thanks to both of you.· Andy's method looks a little cleaner, so I'm gonna give it a shot and see how things go, but appreciate both responses...

Thanks,

Scott