P89V51RD2BN not ready in ISP mode

[Ngoc]

i was using P89V51RD2BN in ISP mode , I use 5 pin TxD,RxD ,Vcc ,Vss , EA and PSEN pull down (in ISP) but appear small window " reset device into ISP mode" . i reset by reset button connect to Vcc and RST pin but it does not work .I can't find any wrong connection , please help me

[erikm]

>>by reset button connect to Vcc and RST pin<<

does not make sence, please explain in detail

Erik

[Jan Waclawek]

1. For the P89V51RD2 programming, you need to use only the Rx and Tx pins (except power supply). Leave  /PSEN  unconnected, and /EA tied to the + supply voltage.
2. Don't use a simple pushbutton (switch) connected between RESET and +Vcc as a reset button. Use a proper reset circuit (e.g. a cheap 7705), they usually have pushbutton inputs. Or use a 3-terminal reset circuit and perform the reset by switching off and on the power source.
The reason is, switches tend to bounce (making short pulses) and most of the '51s tend to do unpredictable things when supplying a shorter than the needed 12- or 24-clock reset.

Jan Waclawek



Post Edited (01-25-05 06:14)

[erikm]

>>and /EA either unconnected or tied to the + supply voltage.<<

Jan, how could you?

CONNECT !EA to Vcc it is mandatory!

Erik

[Jan Waclawek]

Ooooops, sorry, corrected that.

Jan Waclawek