Part Number: TMS320F28P550SJ
Other Parts Discussed in Thread: C2000WARE
Hi expert,
According to the Technical Reference Manual (Rev.D), Figure 4-5 (Overview of SCI Boot Function), it states that:
"Enable the SCIA TX and RX pin functionality and pullups on TX and RX"
However, I would like to clarify the actual behavior of the TX pin during SCI boot.
From C2000Ware boot ROM source (bootloader_sci.c), I can confirm that the RX pin has an explicit pull-up configuration:
GPIO_setPadConfig(gpioRx, GPIO_PIN_TYPE_PULLUP);
But I could not find similar explicit configuration for the TX pin.
In our hardware, we observe that:
- During SCI boot (before autobaud lock), TX line sometimes stays Low
- Adding an external pull-up resistor (10kohm) stabilizes the communication
Based on this, I would like to confirm the following:
1. During SCI boot, does Boot ROM explicitly enable internal pull-up on SCIA_TX pin?
2. If yes, what is the effective strength (resistance or equivalent behavior) of that pull-up?
3. At what point is SCIA_TX driven as an active push-pull UART output (Idle High)?
4. Before SCI TX output becomes active, what is the electrical state of the TX pin (Hi-Z, input, weak pull-up, etc.)?
5. Is external pull-up on TX recommended to guarantee stable SCI boot operation in some conditions?
Any clarification would be greatly appreciated.
Best regards,
Ibuki Endo
