Command Set for EA HMI Series

Short Protocol commands

1. Commands / sending data to display

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

The 16 Bit data are defined as little-endian (Intel format), means that the lower byte need to be sent first.

Example: #XCB20 changes the brightness to 20%. The command need to be terminated with [LF] which is 0x0A.

So the Short Protocol packet starts with DC3 followed by the length (count of data). At the end there's a  CRC16 (CCITT) necessary, calculated with all bytes. Here's a link to an Online-CRC-Calculator.

Hex: 13 07 00 23 58 43 42 32 30 0A 3D CD (here you get it as a file; this may be put to terminal.exe via drag-n-drop)

Example: #XCB80 changes the brightness to 80%.

Hex: 13 07 00 23 58 43 42 38 30 0A FC 0A (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 packet received from 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. The default maximum packet size is 2042 bytes. 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. 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.

10. 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.

CRC-Calculation

A cyclic redundancy check (CRC) is used to calculate the checksum. A common and well known CRC exam is the CRC-CCITT. The starting value is 0xFFFF. The following is a typical C implementation. The functions must be called externally. The checksum must be preallocated with the starting value.

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

//function: buffer2crc16()

//input:    ptr data, ptr CRC, block length

//output:   ---

//descr:   CRC-CCITT of a buffer

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

void buffer2crc16(UBYTE *dat, UINT16 *pCRC, UINT32 len)

{

 while(len--)

   crc16(*dat++, pCRC);

}

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

//function: sp_crc16()

//input:    data, ptr  CRC

//output:   ---

//descr:   CRC_CCITT (x^16+x^12+x^5+1 = 1 0001 0000 0010 0001 = 0x1021

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

void crc16 (UBYTE dat, volatile UINT16 * crc)

{

 register UINT16 lcrc = *crc;

 lcrc = (lcrc >> 8) | (lcrc << 8);

 lcrc ^= dat;

 lcrc ^= (lcrc & 0xFF) >> 4;

 lcrc ^= lcrc << 12;

 lcrc ^= (lcrc & 0xFF) << 5;

 *crc = lcrc;

}