Matrix-orbital VFD2041 User Manual download pdf (Page 22)

3.3 The display module is communicating, however text cannot

be displayed.

• A common cause may be that the contrast settings have been set to low. The solution to this problem

is to adjust the contrast settings. The default setting that will work in most environments is 128.

NOTE Optimal contrastsettings may varyaccordingto factors such as temperature, view-

ing angle and lighting conditions.

If you are unable to resolve any issue please contact Matrix Orbital. See 12.5 on page 49

for contact information.

4 Communications

4.1 Introduction

The commands listed in this chapter describe how to conﬁgure data ﬂow on the VFD2041.

4.1.1 I

C Communication Summary

The VFD2041 is capable of communicating at 100 KHz in I

C mode, with 127 units addressable on a

single I

C communication line. However, in order to communicate via I

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

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

C data lines operate at 5V normally or 3.3V for -1U style units. The

VFD2041 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 VFD2041 should only be sent addresses that are even (LSB is 0). When the

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

C master write. When the I

C master wishes to read the VFD2041, the effective address is $51

(0101 0001), since the LSB has to be 1 for an I

C master read.

If we take a standard Phillips 7 bit address of $45 (100 0101), Matrix Orbital’s VFD2041 would describe

this Phillips I

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

C the VFD2041 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

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

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Matrix-orbital VFD2041 User Manual Page 22

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