that the transmission is over.
The LCD2041 has some speed limitations, especially when run
in I2C mode. Here are some considera-
tions when writing I2C code:
* to be able to read the replies of query commands (eg. cmds 54,
55) the following command must be
sent (only needs to be sent once, so this can be done somewhere
in init): 254 / 160 / 0 this command puts
the reply data in the I2C output buffer instead of the RS232 output buffer. Please note that due to a 16 byte
output buffer, query commands that reply with more than 16 bytes cannot be read (eg cmd Get FileSystem
Directory)
* 3ms delay between the read commands
* 625us delay in between data bytes within a transaction is necessary
* 375us between transactions is necessary
NOTE
These delays are consrevative, and may be decreased based on
performance
4.1.2 I2C Transaction Example
The typical I2C transaction contains four parts: the start sequence, addressing, information, and stop
sequence. To begin a transaction the data line, SDA, must toggle from high to low while the clock line, SCL,
is high. Next, the display must be addressed using a one byte hexadecimal value, the default to write to the
unit is 0x50, while read is 0x51. Then information can be sent
to the unit; even when reading, a command
must ?rst be sent to let the unit know what type of information
it is required to return. After each bit is sent,
the display will issue an ACK or NACK as described above. Finally, when communication is complete, the
transaction is ended by toggling the data line from low to high while the clock line is high. An example of
the use of this algorithm to write a simple “HELLO” message ca
n be seen in 3.
Table 3: I2C Transaction Algorithm
START
Toggle SDA high to low
Address
0x50
Information
0x48 0x45 0x4C 0x4C 0x4F
STOP
Toggle SDA low to high
4.1.3 Serial Communication
In addition to being able to communicate via I2C the LCD2041 communicates natively through the
RS-232 protocol at at a default baud rate of 19,200 bps and is capable of standard baud rates from 9600
to 115,200 bps. Furthermore the LCD2041 is also capable of reproducing any non-standard baud rate in
between using values entered into our baud rate generation algorithm and set through command 164 (0xA4).
The display module communicates at standard voltage levels
of -30V to +30V or at TTL levels of 0 to +5V
by setting the
Protocol Select Jumpers
to TTL.
Matrix Orbital LCD2041
17