4
Communications
4.1
Introduction
The commands listed in this chapter describe how to configure data flow on the LK202-25.
4.1.1
I
2
C Communication Summary
The LK202-25 is capable of communicating at 100 KHz in I
2
C mode, with 127 units addressable on a
single I
2
C communication line. However, in order to communicate via I
2
C you must first ensure that pull up
resistors, with a nominal value of 1K to 10K, are placed on the SCL and SDA communication lines coming
from pins two and three of the Data / Power Connector respectively. Data responses by the module are
automatically output via RS232, in case the host will be querying the module, it is necessary for the host
to inform the module that its responses are to be output via I
2
C. This can be done by sending command
254 /160 / 0 to turn off auto transmission of data in RS232. This will keep the data in the buffer until the
master clocks a read of the slave. The I
2
C data lines operate at 5V normally or 3.3V for -1U style units. The
LK202-25 uses 8-bit addressing, with the 8th or Least Significant Bit (LSB) bit designated as the read/write
bit, a 0 designates a write address and a 1 designates a read address. The default read address of the display
module will be 0x51, whereas the write address is 0x50 by default. This address may be changed by using
cmd 254 / 51 / <address>. The LK202-25 should only be sent addresses that are even (LSB is 0). When the
I
2
C master wishes to write to the display, the effective address is $50 (0101 0000) , since the LSB has to be
0 for an I
2
C master write. When the I
2
C master wishes to read the LK202-25, the effective address is $51
(0101 0001), since the LSB has to be 1 for an I
2
C master read.
If we take a standard Phillips 7 bit address of $45 (100 0101), Matrix Orbital’s LK202-25 would describe
this Phillips I
2
C address as $8A (1000 1010). The read address would be $8B (1000 1011).
The unit does not respond to general call address ($00).
When communicating in I
2
C the LK202-25 will send an ACK on the 9th clock cycle when addressed.
When writing to the display module, the display will respond with a ACK when the write has successfully
been completed. However if the buffer has been filled, or the module is too busy processing data it will
respond with a NAK. When performing a multiple byte read within one I
2
C transaction, each byte read from
the slave should be followed by an ACK to indicate that the master still needs data, and a NAK to indicate
that the transmission is over.
The LK202-25 has some speed limitations, especially when run in I
2
C mode. Here are some considera-
tions when writing I
2
C 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 I
2
C 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
Matrix Orbital
LK202-25
17
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