DS90UB948-Q1: BIST mode

Ryan Wang

Dear expert,

Below description is from UB948 datasheet. But why D_GPIO(0..3) impact BIST?

"Note: Before BIST can be enabled, D_GPIO0 (pin 19) must be strapped HIGH and D_GPIO[3:1] (pins 16, 17, and 18) must be strapped LOW."

Thanks

over 3 years ago

0 Hamzeh Jaradat over 3 years ago

TI__Guru** 115680 points

Hello Ryan,

This is required for the internal logic of the device to be able to work in BIST Mode.

0 Ryan Wang over 3 years ago in reply to Hamzeh Jaradat

TI__Expert 7850 points

Hamzeh,

So how to understand "strapped HIGH "? It has to tie to VCC when at PDB rising edge?

Can customer program them to HIGH/LOW through GPIO registers?

0 Hamzeh Jaradat over 3 years ago in reply to Ryan Wang

TI__Guru** 115680 points

Yes, "strapped HIGH means it needs to be pulled to VCC when PDB is rising. Alternatively You can connect those pins to an MCU to control them.

No, you can't program them through GPIO.

0 Ryan Wang over 3 years ago in reply to Hamzeh Jaradat

TI__Expert 7850 points

Hamzeh,

BTW, if I enable BIST mode from UB941 side, I don't need to enable BIST in UB948 side and don't need to worry about these strap, right?

0 Hamzeh Jaradat over 3 years ago in reply to Ryan Wang

TI__Guru** 115680 points

BIST can and should be only enabled on the DES.

0 Ryan Wang over 3 years ago in reply to Hamzeh Jaradat

TI__Expert 7850 points

Hamzeh,

I'm a little confused.

Below is from UB941 datasheet:

Step 1: The Serializer is paired with an FPD-Link III Deserializer, BIST Mode is enabled through the BISTEN pin
or through register 0x24[0] on the Deserializer or 0x14[0] on the Serializer.

It seems we can enable BIST from UB941?

At this case, should I still worry about these strap at UB948?

0 Hamzeh Jaradat over 3 years ago in reply to Ryan Wang

TI__Guru** 115680 points

Ryan,

you should enable BIST only on DES. When in BIST mode, the 941 register 0x14 shows status only. Bit 0 show BIST enable/disable status. Bit 2 and 1 show which oscillator frequency is used for BIST.

Unfortunately, there is no work around. BIST has to be controlled from DES side.

Hope this is clear!

0 Ryan Wang over 3 years ago in reply to Hamzeh Jaradat

TI__Expert 7850 points

Hamzeh,

Well, it seems we need to update UB941 datasheet. 0x14 register bit 0 BIST_EN is R/W.

And for most system, host is at UB941 side, after host at UB941 side enable BIST through register 0x24[0] on the UB948. Does I2C access from UB941 to UB948 still valid? Otherwise, host cannot disable BIST from UB941 side.