MAX3243: FORCEON pin has no effect on DOUT

Paul Kafig

Other Parts Discussed in Thread: MAX3243

Hello,

I'm using the MAX3243 in an application where the /FORCEOFF pin is tied high (3.3V) and the FORCEON pin is tied low (GND). According to the data sheet, if I have an invalid RS-232 signal on RIN3 (for example, floating), ROUT3 should go into a high-z state. However, when RIN3 in not connected to anything, ROUT3 is driven high. Furthermore, the part behaves the same whether FORCEON is tied high or low.

Am I misunderstanding the data sheet? Thank you for any assistance.

Best regards,

Paul

over 11 years ago

0 Ron Michallick over 11 years ago

TI__Guru**** 164976 points

Paul,

If all RIN are are open, then the DOUT pins go Hi-Z, but the ROUT pins are active.
ROUT pins only go Hi-Z when ~FORCEOFF is low.

0 Paul Kafig over 11 years ago in reply to Ron Michallick

Prodigy 50 points

Hi Ron,

Thanks for the quick reply.

So to be clear, are you saying that ALL RIN lines have to be open in order for any of the DOUT line to go high-z?

The function tables say "each driver" but you're saying that all RIN lines need to be open.

Best regards,

Paul

0 Ron Michallick over 11 years ago in reply to Paul Kafig

TI__Guru**** 164976 points

Paul,

Yes, that is what I stated.

The "EACH DRIVER" table shows HI-Z on DOUT for FORCEOFF low or for "VALID RIN RS232 LEVEL" = No.
For a "No' on RS232 being valid, requires ALL RIN inputs to be invalid.
This allows the MAX3243 to work with remote RS232 systems that do not power all the handshaking lines.

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MAX3243: FORCEON pin has no effect on DOUT