Lpc2000

--- In lpc2000@yahoogroups.com, "jpsg123" <gonzagajohn@h...> wrote:
> I have a problem where the MCU won't boot up. I discovered that if I
have no power on my 
> board but with a serial cable plugged in, the serial driver drives
VCC to -0.5V (max), 
> probable leak since RS-232 Rx input is negative voltage. When I
power up my board, the 
> chip won't boot up. But if I kill power to my board but reapply
power again before VCC 
> drops below 0V, the chip would boot fine (this is possible by the
way because of some 
> large caps on my board, so VCC doesn't immediately go down to 0V).
> 
> Now my question, should the MCU boot up when you power up from
negative VCC as little 
> as -0.5V? Should a reset chip (I'm using TPS3836 3.3) help? In my
case, it doesn't. Thanks.
> 
> -John G-

Hi John,

is there any option to connect ground through your serial cable
between your board and (I guess the PC).  This should help. If not,
unplugging the serial cable before booting should help too. Saw this
kind of problem with negative voltage before and it does screw up the
power on sequence.

Cheers, Bob