use of UART with ISP and RS485

Started by Andert, September 23, 2004, 06:36:50 AM

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I have a systeem with a LPC935. My UART is used by a RS485 module. Can I use my UART for ISP to? And how? Must I disconnect de RS485 module while I'm programming?

Andy Ayre

Probably the easiest way is to use a jumper to enable/disable the RS-232 transeiver and RS-485 transceiver.

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actrually, you do not need to disable anything.  On the 485 the read enable  will be high (disabled) due to the reset and who cares if the 485 transmit.  When read is disabled the read output from the 485 is high and all you need is an NEGATIVE OR ( -08) gate. A resistor on input of the RS232 will force the output from the RS232 transciever high when nothing is connected.  Just tie the two transmit inputs on the transcievers together.

The above assume 485 read enable is driven directly from a port pin and will lead to strange nondestructive events if both cables are attached simultaneously.