Echelon I/O Model Reference for Smart Transceivers and Neuron Chips - Manual (Page 89)

I/O Model Reference 79
Programming Considerations
For bitshift input/output, the data type of the return value for io_in( ), and the
data type of the output value for io_out( ), is an unsigned long.
When using multiple serial I/O devices that have differing bit rates, you must use
the following compiler directive: #pragma enable_multiple_baud. This pragma
must appear prior to the use of any I/O function (such as io_in( ) or io_out( )).
Figure 28. Bitshift Output
Syntax
pin input bitshift [numbits ( const-expr )] [clockedge (+|-)]
[kbaud ( const-expr )] io-object-name ;
pin output bitshift [numbits ( const-expr )] [clockedge (+|-)]
[kbaud ( const-expr )] io-object-name [= initial-output-level ];
pin
An I/O pin. Bitshift input/output requires adjacent pins. The Clock pin is the
pin specified, and the Data pin is the adjacent pin. The pin specification
denotes the lower-numbered pin of the pair and can be IO_0 through IO_6,
IO_8, or IO_9.
numbits ( const-expr )
Specifies the number of bits to be shifted in or out. The const-expr expression
can evaluate to any number from 1 to 31. The default is 16.
Data is shifted in and out with the most significant bit of data first. For the
io_in( ) function, only the last 16 bits shifted in are returned. For the io_out(
) function, after 16 bits, zeros are shifted out.
You can also specify the number of bits to be shifted in the io_in( ) or io_out( )
call. This number temporarily overrides the number specified in the device
declaration, for that one call only.
clockedge (+|-)
For inputs, this option specifies whether the data is read on the positive-
going or negative-going edge of the clock. For outputs, it specifies whether
the data is stable on the positive-going or negative-going edge of the clock.
The default value is [+].