Data transfer

Communication with EA HMI-Series can be done through various hardware interfaces such as RS485, WiFi, LAN and many more. For more details on hardware, baud rate etc. please refer to EA HMI-Series datasheet.

The EA HMI-Series provides different protocols for easy connection to the host system. As standard the proprietary protocol of the EA uniTFT(s)-series is build-in. But various other protocols are available, for example Modbus.

Protocol: Proprietary EA uniTFT(s) Short/Small protocol

The transmission protocol is identical regardless which physical interfaces (RS485, WiFi, LAN...) is used to transfer data from external. All received data packages are collected in internal receive buffer, regardless which interface they come from.

With protocol the data transfer is embedded in a fixed frame including checksum. The EA HMI-Series acknowledges this packet with the character <ACK> (= 0x06) on successful reception or <NAK> (= 0x15) when it detects a faulty checksum or encounters a buffer overflow. In case of a <NAK>, the complete packet is discarded and has to be sent again. An <ACK> only confirms the correct transmission. These data will be put into receive buffer. Note that a syntax check does not take place at this stage.

Two different protocols are implemented, the "Short Protocol" and the "Small Protocol". The Short Protocol works with a CRC16 checksum and allows the transfer of larger data packets. The Small Protocol was implemented mainly for compatibility with the EA eDIPxxx series.

The maximum amount of user data per packet is 2042 bytes or 255 bytes, respectively. Commands that are larger (for example, image or file transfers, #FWD ...) need to be split into several packets. The data in the individual packets is reassembled by the display module after receiving them successfully.

Remark:

The <ACK> has to be read. If the master doesn't receive the acknowledgement, at least one byte is lost. In this case the time-out time needs to be observed before the packet is resent.

The protocol can be disabled on the serial port for testing purposes. To turn off the protocol, pin 22 has to be set low.

Protocol: Modbus

If a module is chosen that provides Modbus protocol: The module supports Modbus communication in the networks based on RS485, WiFi, and Ethernet interfaces. Modbus is a data communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs).

At the moment Modbus RTU is supported.

With the help of the HMIDesigner data mapping is done. The EA HMI-Series acts as Modbus slave only. Detailed explanation about Modbus can be found in this chapter.