Using RS485 in ISP mode

[Mr Canh]

Dir Sir

I want to donwload hex file  for 8951RD2 in long distance ,So I have to convert Max232 to RS485 and use mono circuit to dirve RS485 .In the IAP mode 8951rd2 can communicate easily with PC but in the ISP mode 8951rd2 can not donwload hexfile from FlashMagic.So,how can l solve this prolem ,and I should use which circuit to drive RS485 to program in ISP mode.
I have decreased time delay of mono circuit to minimum by using capacitor
0.001uF and resistance 1 omh.
Please help me

[Andy Ayre]

I am not familiar with RS485 so I cannot help you with your design, however if you have a half duplex connection (for example one wire for data) then you will need to enable the Half Duplex option in the Advanced Options of Flash Magic. That will ensure that only one byte is being transmitted between the device and Flash Magic at any one time.

Make sure you are using the latest version of Flash Magic as there was a recent bug fix to this feature.

[erikm]

I have begged Philips to include a 'transmitting' pin in the ISP ROM code.  The problem with RS485 ISP (which I would love to have) is that you need to enable the transciever transmit from the uC when transmitting.  It is, of course, possible to make something fancy (and only 98% reliable) with a oneshot, but in standard RS485 you use a port pin for this.

If you need to make 485 ISP possible I would suggest that you make the transmit enable selected by a port pin (as standard) when another port pin is low.  Then on ISP, when the pin is high after reset this would enable a oneshot (NOT, absolutely not, retriggerable) that that triggered on the start bit from the uC and was set for 105% of a byte time.  This oneshot would  transmit transmit enable on the 485 transciever  .

Complicated, yes, but I see no other way.

What I have done is to provide a plug for an external 232 transciever for ISP purposes.

Remember that the proper name for the chip is 'one shot in your own foot'

Erik

[Canh]

Thanh for your help .
I want to know that ISP mode using FULL DUPLEX or Half duplex.If program ASM in MCU 89rdxx use half duplex I can change Option of Flagmagic.So,you can show me how to read instruction of ISP
ThanhkS

[Andy Ayre]

The bootloader echoes back any character it receives immediately. Once a full hex record has been sent, it sends out the response. So as long as you send once character at a time to the bootloader, you can say it is half duplex in operation.

By default, Flash Magic talks to the bootloader using full duplex, as that is much quicker and more efficient than half duplex.