Protocol / Data transfer
The transmission protocol is identical regardless of which of the 4 serial interfaces is used to transfer data from the higher-level controller. The hardware circuit for each interface varies, which is described under the chapter "serial interfaces".
The data transfer is embedded in a fixed frame with checksum. The EA uniTFTs-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. A syntax check does not take place.
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 ...) must be split into several packets. The data in the individual packets is reassembled by the display module after receiving them successfully.
The <ACK> has to be read (SPI and I²C). 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 14 has to be set low (see pin assignment).