ADUC845 Bootloader

Question

Good morning to everyone: 
 I have a prototype made on the basis of the evaluation board of micro ADUC845/6/7 in which I have added a driver 485 and an operational amplier in the DAC output. Below is the drawing. 
 The problem I find that putting the PSEN pin low level (GND) and do the reset, the bootloader does not start. I'm using the original TTL to 232 cable of the evaluation board to communicate with the PC (I take the power for this cable from AVDD and GND. 
 I have the same configuration (I think) mounted on the evaluation board and everything works fine. 
 What could be wrong? I would appreciate your help.

ADIApproved · Accepted Answer

Have this board ever been working ? Do you see any signal on TX if you put the ADuC845 into download mode ? Can you check on a second board or replace the ADuC845 ?)

ADIApproved · Answer

The only idea I have is that something with the RS485 transceiver is wrong or with the /RE - you may check this signals that the RX pin on the ADuC845 is only driven from the RS232 transceiver - but anyway this is critical and can cause problems if you connect the PC-Interface-Cable with the RS232 transceiver integrated before you put the RS485 receiver output into High-Z mode.

Electronic Design Services - PartnerZone

Products Mentioned

ADUC845 Bootloader