Pololu Qik 2s9v1 Manuel d'utilisateur télécharger pdf (Page 12)

4. Serial Interface

You can use the serial interface for three general purposes: querying the qik for information, setting its

configuration parameters, and sending it motor commands. Motor commands are strictly one-way; all other

commands result in the qik’s responding with a single byte that either represents information that has been

requested or feedback on the effect of the issued command.

4.a. TTL Serial

The qik requires a logic-level (0 – Vcc, or “TTL”), non-inverted serial input connected to its serial receive line

RX. The serial interface is asynchronous, meaning that the sender and receiver each independently time the serial

bits; asynchronous serial is available in computer serial ports (though at non-TTL levels) and as hardware modules

called “UARTs” on many microcontrollers. Asynchronous serial output can also be “bit-banged” by a standard

digital output line under software control. The data format is 8 data bits, one stop bit, with no parity. The diagram

below depicts a typical asynchronous, non-inverted TTL serial byte.

A non-inverted TTL serial line has a default (non-active) state of high. A transmitted byte begins with a single

low “start bit”, followed by the bits of the byte, least-significant bit (LSB) first. Logical ones are transmitted as

high (Vcc) and logical zeros are transmitted as low (0 V), which is why this format is referred to as “non-inverted”

serial. The byte is terminated by a “stop bit”, which is the line going high for at least one bit time. Because each

byte also requires start and stop bits, each byte takes 10 bit times to transmit, so the fastest possible data rate

in bytes per second is the baud rate divided by ten. At the maximum baud rate of 38,400 bits per second, the

maximum realizable data rate, with a start bit coming immediately after the preceding byte’s stop bit, is 3,840

bytes per second.

The voltage on the RX pin should not exceed Vcc. The qik will provide logic-level serial output on its serial

transmit line TX in response to commands that request information. Information requests aways result in the

transmission of a single byte per request. If you aren’t interested in receiving feedback from the qik, you can leave

this line disconnected.

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Pololu Qik 2s9v1 Manuel d'utilisateur Page 12