TCA6424A: Data Transfer Strobe timing

Steve Widener

Part Number: TCA6424A

On the TCA6424A, the block diagram in Figure 18, it shows a Write Pulse and a Read Pulse going to the I/O port. I am trying to determine when in the data transfer cycle these strobes are asserted, and do they assert once per data transfer cycle to sample all port data at once, or are the IO Port contents shifted out sequentially with multiple Write/Read Pulses per successive SCLs?

over 3 years ago

0 BOBBY over 3 years ago

TI__Mastermind 49410 points

For write transactions this would be under the timing parameter t_pv which can be seen in figure 16 on the rising ACK clock pulse is received for the particular written data (all bits of that port for that specific byte).

For a read transaction, this would be under the timing parameter t_ps in which the data is sampled on all ports at the same time on the rising clock edge of the ACK pulse. (Also figure 16)

thanks,

-Bobby

0 Steve Widener over 3 years ago in reply to BOBBY

TI__Genius 9595 points

Thanks!

Additionally, if you could clarify if there is any adverse effect on the initialization of the part if it’s powered up without a reset being applied.

0 BOBBY over 3 years ago in reply to Steve Widener

TI__Mastermind 49410 points

Hey Steve,

Are you implying reset is floating? or Is it referenced to something like Vcc or another rail of some sort?

-Bobby

0 Robert McNally over 3 years ago in reply to BOBBY

Prodigy 30 points

The reset line should be pulled to Vcc.

0 Robert McNally over 3 years ago in reply to Robert McNally

Prodigy 30 points

Hi Bobby, just following up.... based on my feedback that the reset line was tied to VCC, thus no "reset" exercised at power on, does this cause any indeterminate behavior with device initialization until programmed via I2C?

0 Robert McNally over 3 years ago in reply to BOBBY

Prodigy 30 points

0 BOBBY over 3 years ago in reply to Robert McNally

TI__Mastermind 49410 points

Hey Robert,

The reset pin is typically tied to the VCC rail. When the device powers on for the first time, it does receive a reset pulse through its power up circuit so there shouldn't be any indeterminate behavior upon power up.

If you are seeing some kind of issue where the device powers up in a different state than default, I would suggest double checking ur Vcc ramp and making sure it meets the requirements set in section 10 of the datasheet.

-Bobby

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TCA6424A: Data Transfer Strobe timing