Hardware configuration to select boot mode

SPC560P34x, SPC560P40x

6/11

Doc ID 022359 Rev 2

1.2

Autobaud feature

SPC560P34x/SPC560P40x devices implement the autobaud feature via FlexCAN or

LINFlex selecting the active serial communication peripheral by means of an autoscan

routine.

When autobaud configuration is selected by ABS and FAB pins, the autoscan routine starts

and listens to the active bus protocol. Initially the LinFlex_0 RX pin and FlexCAN_0 RX pin

are configured as GPIO inputs:

●

for LQFP100 internal weak pull-up enabled for both RX pins,

●

for LQFP64 internal weak pull-up enabled only for FlexCAN_0 RX pin.

The autoscan routine waits in polling for the first LOW level to select which routine will be

executed:

●

FlexCAN Autobaud routine

●

LinFlex Autobaud routine

Then the measurement baud rate is computed to configure the serial communication at the

right rate. In the end of baud rate measurement, LinFlex_0 RX pin and FlexCAN_0 RX pin

switches to work as dedicated pin.

Baud rate measurement is using the System Timer Module (STM) which is driven by the

system clock. Measurement itself is performed by software polling the related inputs as

general purpose IO’s, resulting in a detection granularity that is directly related to the

execution speed of the software.

One main difference of the autobaud feature is that the system clock is not driven directly by

the external oscillator, but it is driven by the FMPLL output. The reason is that to have an

optimum resolution for baud rate measurement, the system clock needs to be nearer to the

maximum allowed device’s frequency.

This is achieved with the following two steps:

1.

using the Clock Monitor Unit (CMU) and the internal RC oscillator (IRC), the external

frequency is measured using the IRC as reference to determine this frequency.

2.

Based on the result of this measurement, the FMPLL is programmed to generate a

system clock that is configured to be near, but lower, to the maximum allowed

frequency.

After setting up the system clock, the BAM autoscan code configures the FlexCAN RX pin

(B[1] on all packages) and LINFlex RX pin (B[3] on LQFP100 or B[7] on LQFP64) as GPIO

inputs and searches for FlexCAN RX pin level to verify if CAN is connected or not.

B[3](2)

LIN_0 RX

-

B[7](3)

LIN_0 RX

29

1.

Weak pull down during reset.

2.

SPC560P34x/SPC560P40x LQFP100 package uses only PAD B[3] - pin 80 for boot via LINFLEX

3.

SPC560P34x/SPC560P40x LQFP64 package uses only PAD B[7] - pin 20 for boot via LINFLEX

Table 2.

SPC560P34x/SPC560P40x boot pins (continued)

Port pin

Function

Pin

64-pin

100-pin