Echelon I/O Model Reference for Smart Transceivers and Neuron Chips - Manual (Page 57)

I/O Model Reference 47
This argument has a minimum value of 7.2 μs ( t_low = 1) from the
start of t
LOW
. The incremental resolution of t_low is 3 μs, so the
control range is 4.2 + n * 3 (in μs) where n is 1 to 255, and a t-low
value of 0 is equivalent to n=256.
• t-rdi
The length of t
RDI
. This is the interval where the Neuron firmware
asserts either a low or a high on the 1-Wire bus, depending on the
output data bit polarity. For read operations, this data polarity is
always high. This argument has a minimum value of 7.8 μs ( t-rdi = 1)
from the start of t
RDI
. The incremental resolution of t-rdi is 3 μs, so
the control range is 4.8 + n * 3 (in μs) where n is 1 to 255, and a t-rdi
value of 0 is equivalent to n=256.
• t-wrd
Start of t
WRD
(end of t
RDI
). This is the point where the Neuron
firmware samples the 1-Wire bus for the input data bit, and occurs
for both read and write operations. This argument has a minimum
value of 15 μs ( t-wrd = 1) from the start of t
WRD
. The incremental
resolution of t-wrd is 3 μs, so the control range is 12 + n * 3 (in μs)
where n is 1 to 255, and a t-wrd value of 0 is equivalent to n=256.
At the end of t-wrd , the Neuron firmware releases the 1-Wire bus.
io-object-name
A user-specified name for the I/O object, in the ANSI C format for variable
identifiers.
Usage
unsigned int count ;
unsigned int touch-buffer [ buffer-size ];
io_out( io-object-name , touch-buffer , count );
io_in( io-object-name , touch-buffer , count );
The touch-buffer can be any type or structure, and the type of the touch-buffer
parameter is const void*. The address of the buffer is passed to the io_out( )
and io_in( ) functions. There are several additional support functions for the
Touch I/O object: touch_reset( ), touch_byte( ), touch_bit( ), touch_first( ),
touch_next( ), crc8( ), and crc16( ).
For Neuron Chips and Smart Transceivers that include system firmware version
18 or later, there are other additional support functions for the Touch I/O model:
touch_reset_spu( ), touch_byte_spu( ), touch_read_spu( ), touch_write_spu( ), and
crc16_ccitt().
int touch_reset( io-object-name );
The touch_reset( ) function asserts the reset pulse. The function returns a 1
value if a presence pulse was detected, or a 0 value if no presence pulse was
detected, or a -1 value if the 1-Wire bus appears to be stuck low. The operation of
this function is controlled by several timing constants:
• The reset pulse period, 500 μs.
• After the reset pulse period, the Neuron firmware releases the 1-Wire bus
and waits for the 1-Wire bus to return to the high state. This period is