EA uniTFT Series

Small Protocol commands

1. Commands / data send to module

This protocol command transfers data to the display. Several graphics commands can be packaged in a protocol package. If the data is larger than the maximum packet size, the data can be split into several packets. The module reassembles the individual data packets.

Example: #XCB25 changes the brightness into 25%. The command need to be terminated with [LF] which is 0x0A.

So the Small Protocol packet starts with DC1 followed by the length (count of data). At the end there's a bcc (8 bit summary, modulo 256) necessary, calculated with all bytes.  Here's a link to an Online-CRC-Calculator.

Hex: 11 07 23 58 43 42 32 35 0A 89 (here you get it as a file; this may be put to terminal.exe via drag-n-drop)

Example: #XCB75 changes the brightness into 75%.

Hex: 11 07 23 58 43 42 37 35 0A 8E (here you get it as a file)

2. Request data of send buffer

If data is generated in the module, it is stored in the module's send buffer. The data can be requested via the serial interfaces. Whether data is available can be monitored via the pin 20 SBUF, or the higher-level controller can cyclically poll the data.

3. Repeat last data packet

If a received packet of the module is faulty (wrong length or checksum) it can be requested again:

4. Request buffer information

This command queries whether user data is ready (= Pin20 SBUF) and also indicates how much free space is left in the device's receive buffer.

5. Protocol settings

This can be used to limit the maximum packet size that the display may send. As default a packet size with up to 2042 bytes of user data is set. Furthermore, the time-out can be set in 1 / 1000s. The time-out is activated when individual bytes have been lost. After the timeout, the entire packet must be retransmitted.

6. Protocol information

Request protocol settings (see 5.).

7. RS485 address select / deselect

With this command, a module can be selected or deselected on the RS485 bus. By default, the module with address 7 is always active.

8. RS485 enable signal - delay

Some RS485 masters take some time to change the enable signal, e.g. to switch from write to read mode. In order to enable successful communication with these devices, this command can be used to delay switching to write mode.

9. Request interface exclusively

All 4 serial ports are handled in parallel and equivalently after reset. To ensure that a sequence of protocol packets is executed without interruption, the other serial interfaces can be disabled so the active interface can communicate with the module exclusively. This is useful, for example, for a project update via USB.

10. Break-Command, Break / Stop execution

If a continuous loop has been programmed in a macro or if a normal process flow is blocked, this command can be used to interrupt and quit. This command is also suitable for update processes.

11. Hardware Reset

The module is restarted with this protocol command. Depending on the parameter, various start options can be selected to automatically run after the reset.

BCC-Calculation

The calculation of the checksum requires a simple 8-bit sum test (modulo 256). The following is a typical C implementation.

//----------------------------------------------------------------------------

//function: buffer2bcc()

//input:    ptr data, block length

//output:   Byte bcc

//descr:    calculate bcc for a buffer

//----------------------------------------------------------------------------

UBYTE buffer2bcc(UBYTE *dat, UBYTE len)

{

 UBYTE bcc = 0;

 while(len--)

   bcc += *dat++;

 return bcc;

}