M Lionel

Problem to write TJA1100 registers

Discussion created by M Lionel on Jan 12, 2018



I use a TJA1100 (PHY BroadR Reach) and I communicate beetwen MCU MPC5748G and TJA1100 with the SMI link : signals MDIO and MDC.

I can read all the internal registers inside the TJA1100 without any problem => I read the right value for PHY_ID, TYPE_NO, PHYAD[4:0], ...

But I can't write these registers - which can be in R/W - and I can't change the "CONFIG_EN" bit in the Extented Control register (17), too.

The 2 signals MDIO and MDC (2.5 MHz) seems OK on scope for Read (0x10) and Write (0x01) operations.


After reading the TJA1100 registers, the TJA1100 is in the following configuration:

Basic Control Register (0) = 0x2100  => POWER_DOWN = 0(Normal Operation) , ISOLATE = 0 (normal operation)

PHY identification register 1 (2) = 0x0180

PHY identification register 2 (3) = 0xDC41

PHY identification register 3 (16) = 0x00A9


LINK_CONTROL = 0 (disable)

POWER_MODE = 1100 (Standby Mode)




MASTER_SLAVE = 0 or 1 (depending of my hardware configuration)

AUTO_OP = 0 (managed operation)

PHY_STATE = 000 (Idle).


Why it's not possible to write inside TJA1100 registers and not possible to change the "CONFIG_EN" bit (register 17) ?


Thanks for your futurs answers (or questions).