Matrix-orbital VFD2041 User Manual download pdf (Page 23)

that the transmission is over.

The VFD2041 has some speed limitations, especially when run in I

C mode. Here are some considera-

tions when writing I

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

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

NOTE These delays are consrevative, and may be decreased based on performance

4.1.2 I

C Transaction Example

The typical I

C 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 ﬁrst 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 can be seen in 3.

Table 3: I

C 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 I

C the VFD2041 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 VFD2041 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.

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Matrix-orbital VFD2041 User Manual Page 23