Monitor HC908q

[chempi]

Hi everyone

I recently bought a HC908qy4, And I made a circuit to get the monitor mode following the AN2305 and 2317 application note.

I could achieve the connection between the Pemicro software and the hc908qy4, but I after I programmed the micro, i could not achieve the connection again, I checked and rechecked the connection, but i could not achieve anything, but when I replace de Vtst voltage from the max232 and zener diode (9.1V) with an external source of Vtst (lm78l08) I get the connection again.

I don´t understand what this happen, I someone can help me, I would appreciate it

Andres

[eckhard]

Hello,

the blank chip is using the forced monitor mode, there is no high voltage needed on IRQ.

The programmed chips need Vtst apllied on the IRQ Pin. Sometimes the problem is that the voltage of the MAX232 charge pump is rising too slow to get Vtst applied early enough in the reset sequence. A workaround is to put a delay into Power on Reset. You can do that by keeping a reset button pushed or by adding a RC combination to the reset pin. This works fine for me.

Eckhard

[yb]

Hi,

Try a 8.2V zener to replace your 9.1V.

The MAX232 deliver sometimes less than 10V.

Regards,

Yvan