UM0932 datasheet(14/43 Pages) STMICROELECTRONICS

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Host interface

UM0932

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DocID17385 Rev 3

The UART interface has two data channels:



TXD carries data from the ST7580 to the host



RXD carries data from the host to the ST7580

A local request input signal is implemented on the T_REQ pin.

ST7580 UART is a half duplex asynchronous serial port without hardware control flow.

UART settings used are:



Half duplex mode



Standard NRZ bit coding



LSBit first transmission: the bits within each byte are sent LSBit to MSBit



The exchanged frames are composed of characters



A single character is composed of 1 start bit, 8 data bits and 1 stop bit



0-5 V or 0-3.3 V levels on TXD, RXD, T_REQ signals.

Figure 7 shows the character format:

Figure 7. Local port character format

3.2

Communication protocol

The host interface process implemented in the ST7580 device performs the following tasks:



The frame format definition



The reception mechanism: the UART standard on half duplex data channel is

implemented and collisions are avoided



The acknowledgement to received frames



The timeout management



The error checking: length, syntax and checksum field of a received frame are

controlled and a repetition is requested in case of error.

3.2.1

Frame types

A frame is a sequence of one or more characters encapsulating a data exchanged between

the ST7580 device and the host controller. The communication protocol defines several

frame formats for the different steps of the communication protocol (access to ST7580

services, acknowledgement, device status).

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