Echelon I/O Model Reference for Smart Transceivers and Neuron Chips - Manual (Page 115)

I/O Model Reference 105
STA
RT
STA
RT
STO
P
Figure 38. Serial Output Timing
Table 38. Serial Output Latency Values for Series 3100 Devices
Symbol Description Typical at 10 MHz
t
fout
Function call to start bit 79 μs
t
ret
Return from function 10 μs
The duration of this function call is a function of the number of data bits
transferred and the transmission bit rate. For example, to output 100 bytes at
300 bits/second requires a time duration of (100 x 10 x 1/300) + t
fout
+ t
ret
.
Programming Considerations
The format for data frame transfer is fixed: one start bit, followed by eight data
bits (least significant bit first), followed by one stop bit. The input serial I/O
object waits for the start of the data frame to be received for up to the time it
would take to receive 20 characters before timing out and returning a zero. Input
is terminated when either the total count in bytes is received, or the amount of
time it would take to receive 20 characters has passed with no data received. The
input serial I/O model stops receiving data on invalid stop bit. At 2400 bps, the
input timeout is 83 ms.
Unlike the SCI and SPI I/O models, which are available only for certain Neuron
Chip models, the serial input/output model does not require special hardware and
is available for all Neuron Chip models.
Both serial input and output models are purely software I/O models, with no
hardware support other than the physical I/O pins. The serial stream is read in
and transmitted out using CPU timing. See the sci I/O model for an equivalent
I/O object that uses UART hardware on certain Smart Transceivers and Neuron
Chips. The following issues should be considered when using the serial I/O
model:
• The io_out( ) function is a blocking function, so the function does not
return until the entire data set is transmitted.