NHD-0420DZ-NSW-BBW want to ignore characters

[OrrisD]

We need to keep the serial data stream to the LCD active at all times,
even when there is no need to send information to the LCD.
We would like to send "filler" characters or sets of characters
between control sequences and displayable characters.
Is there a character series that is ignored by the LCD,
for example, would 0xFE, 0x00 work?

[perky]

Can you determine in the stream whether the data is meant to be displayed or not? the ST7066 controller has an extended 80*8 DDRAM area and says you can use an area of DDRAM not used for display to store general data, all you would need to do is re-direct the writes to one of those areas.

What is the reason you want to do this? Is it a timing issue, or maybe you don't want to put any buffering in the way?
Mark.

[OrrisD]

The reason we want to keep the serial data constantly running is that the LCD is at the midpoint of a half-duplex data link.
Data comes from the host to a switch box that can send the switch configuration back to the host in between the host bytes.
We want the LCD to display status info. from the host, but NOT be affected by traffic from the host that is used to provide sync characters.  We run the LCD at 57,600 baud and send out a character from the host every millisecond. This gives plenty of time for the switch box to send back information to the host in between host outgoing traffic.  Host data is relatively infrequent, and the switch box loses track of time relative to the one millisecond ticks if its timer is not refreshed often enough.   We are presently sending a 0xFE,0x0F sequence as a filler and have found out that the LCD ignores it. 
The suggestion about unused memory space in the LCD is a good one. We'll try that next. Thanks.

[perky]

OK, if I understand you correctly you want the LCD to 'snoop' on the serial stream and be completely agnostic to the sync protocol. Presumably this means the packets that you send contain a start address for each packet (the first character position for that chunk of data) which you would need in order for the display not to increment its address counter past the displayable area. If that's the case changing the address to somewhere in the non-displayable area should work, and that address could be the flag that it's a sync packet that indicates that the switch has to send a response back to the host. Is that correct?
Mark.