Connecting 2 LCD's together

[RF]

Hi,

My project requires 2 off 16x2 LCD’s (HD44780 based) to be displayed together ie. the same information is displayed on both LCD’s in 4-bit databus mode. Without connecting the hardware, can anyone confirm whether the following lines can be connected together?

LCD1 LCD2 16F876A
---------------------------------------
RS to RS to TBD
E to E to TBD
R/W to R/W to TBD
D4 to D4 to TBD
D5 to D5 to TBD
D6 to D6 to TBD
D7 to D7 to TBD

Thanks in advance.
RF
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516286

[R.J.Hamlett]

:=Hi,
:=
:=My project requires 2 off 16x2 LCD’s (HD44780 based) to be displayed together ie. the same information is displayed on both LCD’s in 4-bit databus mode. Without connecting the hardware, can anyone confirm whether the following lines can be connected together?
:=
:=LCD1 LCD2 16F876A
:=---------------------------------------
:=RS to RS to TBD
:=E to E to TBD
:=R/W to R/W to TBD
:=D4 to D4 to TBD
:=D5 to D5 to TBD
:=D6 to D6 to TBD
:=D7 to D7 to TBD
:=
:=Thanks in advance.
:=RF

Yes, you can drive two displays like this. However there are some 'caveats'. You have to ensure that the driver is written, to allways allow enough time for each operation (you cannot 'poll' the busy flag on the displays), and you may well find there is a problem with noise on the second display (depends on the enviroment, and the wiring length).
I have done this in the past, with 8bit data, and using an interrupt driven 'sender', which transferred just one character every 1/100th second. This is slow enough, that the 'worst case' timing (usually a CLS operation), is still executed before the next character is transferred.

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516288

[RF]

:=:=Hi,
:=:=
:=:=My project requires 2 off 16x2 LCD’s (HD44780 based) to be displayed together ie. the same information is displayed on both LCD’s in 4-bit databus mode. Without connecting the hardware, can anyone confirm whether the following lines can be connected together?
:=:=
:=:=LCD1 LCD2 16F876A
:=:=---------------------------------------
:=:=RS to RS to TBD
:=:=E to E to TBD
:=:=R/W to R/W to TBD
:=:=D4 to D4 to TBD
:=:=D5 to D5 to TBD
:=:=D6 to D6 to TBD
:=:=D7 to D7 to TBD
:=:=
:=:=Thanks in advance.
:=:=RF
:=
:=Yes, you can drive two displays like this. However there are some 'caveats'. You have to ensure that the driver is written, to allways allow enough time for each operation (you cannot 'poll' the busy flag on the displays), and you may well find there is a problem with noise on the second display (depends on the enviroment, and the wiring length).
:=I have done this in the past, with 8bit data, and using an interrupt driven 'sender', which transferred just one character every 1/100th second. This is slow enough, that the 'worst case' timing (usually a CLS operation), is still executed before the next character is transferred.
:=
:=Best Wishes

Thanks for your reply. The second LCD will be upto 10 metres away and therefore I assume that all the delays within the CCS lcd.c functions will have to be increased. I may give it a try. I think I might get rid of the second LCD and connect the analog signal to a Lascar DPM (digital voltmeter with built-in A/D). The advantage of using the DPM is that there are less wires to deal with.
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516304

[R.J.Hamlett]

:=:=:=Hi,
:=:=:=
:=:=:=My project requires 2 off 16x2 LCD’s (HD44780 based) to be displayed together ie. the same information is displayed on both LCD’s in 4-bit databus mode. Without connecting the hardware, can anyone confirm whether the following lines can be connected together?
:=:=:=
:=:=:=LCD1 LCD2 16F876A
:=:=:=---------------------------------------
:=:=:=RS to RS to TBD
:=:=:=E to E to TBD
:=:=:=R/W to R/W to TBD
:=:=:=D4 to D4 to TBD
:=:=:=D5 to D5 to TBD
:=:=:=D6 to D6 to TBD
:=:=:=D7 to D7 to TBD
:=:=:=
:=:=:=Thanks in advance.
:=:=:=RF
:=:=
:=:=Yes, you can drive two displays like this. However there are some 'caveats'. You have to ensure that the driver is written, to allways allow enough time for each operation (you cannot 'poll' the busy flag on the displays), and you may well find there is a problem with noise on the second display (depends on the enviroment, and the wiring length).
:=:=I have done this in the past, with 8bit data, and using an interrupt driven 'sender', which transferred just one character every 1/100th second. This is slow enough, that the 'worst case' timing (usually a CLS operation), is still executed before the next character is transferred.
:=:=
:=:=Best Wishes
:=
:=Thanks for your reply. The second LCD will be upto 10 metres away and therefore I assume that all the delays within the CCS lcd.c functions will have to be increased. I may give it a try. I think I might get rid of the second LCD and connect the analog signal to a Lascar DPM (digital voltmeter with built-in A/D). The advantage of using the DPM is that there are less wires to deal with.

If it is only an analog signal, go the second route. 10m, is a long way, and you would really have to look at using some form of terminated transmission line to reliably send the signals this far. However don't send the signal as a voltage, but build a simple V-I converter (you don't have to go to the complexity of a system like 4-20mA, with the current offset from ground). Instead just use an op-amp, to drive the voltage into the line, and have the second pin of the connection, connected to a fixed resistor (perhaps 100ohm), then have the feedback loop of the op-amp, set to maintain the required voltage across this resistor. Add an identical resistor at the DPM, and you can have the same voltage developed here, despite the line voltage drops. :-)

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516305

[RF]

:=:=:=:=Hi,
:=:=:=:=
:=:=:=:=My project requires 2 off 16x2 LCD’s (HD44780 based) to be displayed together ie. the same information is displayed on both LCD’s in 4-bit databus mode. Without connecting the hardware, can anyone confirm whether the following lines can be connected together?
:=:=:=:=
:=:=:=:=LCD1 LCD2 16F876A
:=:=:=:=---------------------------------------
:=:=:=:=RS to RS to TBD
:=:=:=:=E to E to TBD
:=:=:=:=R/W to R/W to TBD
:=:=:=:=D4 to D4 to TBD
:=:=:=:=D5 to D5 to TBD
:=:=:=:=D6 to D6 to TBD
:=:=:=:=D7 to D7 to TBD
:=:=:=:=
:=:=:=:=Thanks in advance.
:=:=:=:=RF
:=:=:=
:=:=:=Yes, you can drive two displays like this. However there are some 'caveats'. You have to ensure that the driver is written, to allways allow enough time for each operation (you cannot 'poll' the busy flag on the displays), and you may well find there is a problem with noise on the second display (depends on the enviroment, and the wiring length).
:=:=:=I have done this in the past, with 8bit data, and using an interrupt driven 'sender', which transferred just one character every 1/100th second. This is slow enough, that the 'worst case' timing (usually a CLS operation), is still executed before the next character is transferred.
:=:=:=
:=:=:=Best Wishes
:=:=
:=:=Thanks for your reply. The second LCD will be upto 10 metres away and therefore I assume that all the delays within the CCS lcd.c functions will have to be increased. I may give it a try. I think I might get rid of the second LCD and connect the analog signal to a Lascar DPM (digital voltmeter with built-in A/D). The advantage of using the DPM is that there are less wires to deal with.
:=
:=If it is only an analog signal, go the second route. 10m, is a long way, and you would really have to look at using some form of terminated transmission line to reliably send the signals this far. However don't send the signal as a voltage, but build a simple V-I converter (you don't have to go to the complexity of a system like 4-20mA, with the current offset from ground). Instead just use an op-amp, to drive the voltage into the line, and have the second pin of the connection, connected to a fixed resistor (perhaps 100ohm), then have the feedback loop of the op-amp, set to maintain the required voltage across this resistor. Add an identical resistor at the DPM, and you can have the same voltage developed here, despite the line voltage drops. :-)
:=
:=Best Wishes

Yes, you are right. The V-I and I-V method is a good idea to overcome the problem of line voltage drop. Thanks again.
___________________________
This message was ported from CCS's old forum
Original Post ID: 144516307