Echelon I/O Model Reference for Smart Transceivers and Neu Manual de usuario descargar pdf (Pagina 115)

I/O Model Reference 105

START

STOP

Figure 38. Serial Output Timing

Table 38. Serial Output Latency Values for Series 3100 Devices

Symbol Description Typical at 10 MHz

fout

Function call to start bit 79 μs

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.

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Echelon I/O Model Reference for Smart Transceivers and Neu Manual de usuario Pagina 115