User's Manual

1 DATECS DPP-450 User manual
21
2: Send data
3: Request data
>4: Application specific
Status: One byte:
0 1
Bit 0
No error Error occured
Bit 1
ACK (Packet accepted) NACK (Packed not accepted)
Bit 2
Channel and command OK Wrong channel or command
Bit 3
Battery OK Low battery
Bit 4
Printing head OK Printing head too hot
Bit 5
Paper OK Out of paper
Bit 6
Not defined
Bit 7
Printer ready Printer busy
Bit 7 is set, if:
• There are unprinted lines in the print buffer.
• There are bytes in the print buffer.
• The printer is executing a macro.
• The printer is executing selftest.
• The button <LF> is pressed – feeding paper.
LenHi: High byte of data length of data. 00h to 08h.
LenLo: Low byte of data length of data. 00h to FFh.
Data: 256*LenHi +LenLo data bytes.
The maximum packet length is 2048 bytes.
The answer differs from the command by bit 7 (MSB) in the channel number. If
bit 7 is 0 then it is a command, if it is 1 then it is a response. Bit 0 in the status
byte shows if there was an error accepting or processing the data block. If this bit
is 1 the other bits show the type of the error.
The printer never issues a transmission by itself. It always responds as an
answer to a command. The communication goes like this:
Host – command, Printer – answer; Host – command, Printer – answer; etc.
The defined channels are:
1 Printer.
16 (10h) Optional card reader.
Commands for the printer channel (1):
Command 2 Send data
The data is copied into the printer’s print buffer. If there’s not
enough space into the print buffer the packet is rejected, and a status
byte with value 3 is returned in the answer.
Command 3 Receive data
If there is data to be transmitted from the printer to the host, it is
transmitted in the data field of the packet, otherwise an empty packet
is received. The application must take care to get the data fast enough
from the output buffer or the data may be corrupt.