2010-11-11, 11:52:13
(This post was last modified: 2010-11-11, 14:14:24 by vmsbarbosa.)
I didn'nt have time yet to explore this on firmware, but bootloader start-up should be independent of the logic level input at RX. It shouldn't jump if a logic level "0" is present at RX on start-up or after a reset.
If this is important to the user and the user choose the hardware solution (the placement of a pullup resistor at RX), careful has to be taken with the pullup resistor value:
With a value very big, as 100K or more, associated with the capacity value of the pcb trace, the voltage don't have or may not have time enough to rise to a logic level "1" in a short time of a few ms, from power-up to the moment when RX is read by the first time. This effect is only present on power-up, but on a normal reset this is solved.
With a smaller value, 10K (on my board), the power-up problem was solved, as RC time contant is smaller. Capacity of the pcb traces depend on the pcb design and this value could not work on other designs.
This could not be important for the most users, as in general RX/TX lines are connected to a transceiver (RS232 or RS485 or...) and the output of this devices is a logic level "1" in the absence of communications (the start-bit on UART protocol is recognized as fall-down edge) but surprises could happen.
Although this, the bootloader is working perfectly in my application.
Thanks for this bootloader!
I will try to fix this on the firmware.
Vitor
If this is important to the user and the user choose the hardware solution (the placement of a pullup resistor at RX), careful has to be taken with the pullup resistor value:
With a value very big, as 100K or more, associated with the capacity value of the pcb trace, the voltage don't have or may not have time enough to rise to a logic level "1" in a short time of a few ms, from power-up to the moment when RX is read by the first time. This effect is only present on power-up, but on a normal reset this is solved.
With a smaller value, 10K (on my board), the power-up problem was solved, as RC time contant is smaller. Capacity of the pcb traces depend on the pcb design and this value could not work on other designs.
This could not be important for the most users, as in general RX/TX lines are connected to a transceiver (RS232 or RS485 or...) and the output of this devices is a logic level "1" in the absence of communications (the start-bit on UART protocol is recognized as fall-down edge) but surprises could happen.
Although this, the bootloader is working perfectly in my application.
Thanks for this bootloader!
I will try to fix this on the firmware.
Vitor