4.16.3 Transmit Jabber

Network communication may become blocked if a device fails in such a mode as to become stuck in the transmit state continually driving the shared bus, i.e., “jabber”. To help guard against this failure mode the LAN8670/1/2 is designed with a transmit jabber watchdog. Should the PCS block remain in the transmit state for longer than 2 ms the jabber watchdog will trigger. When the transmit jabber watchdog triggers, the PCS will transmit special ESDERR End-of-Stream Error ESDJAB End-of-Stream Jabber Delimiter codes to the network followed by disabling the transmitter. Additionally, the Jabber Detection Status (JAB_DET) bit in the Clause 22 Basic Status (BASIC_STATUS) register will be set along with the Transmit Jabber Status (TXJAB) status bit in the Status 1 (STS1) register. If the Transmit Jabber Status interrupt status is not masked via the Transmit Jabber Interrupt Mask (TXJABM) bit in the Interrupt Mask 1 (IMSK1) register, the IRQ_N pin will assert.

Once a transmit jabber condition has been detected, the PCS will wait 16 ms before attempting another transmission. The transmit jabber watchdog is reset between packets transmitted with PLCA burst mode enabled.

Since a device terminates a jabber transmission with a special ESDJAB End-of-Stream Jabber Delimiter code, all receiving devices can detect when a remote device has jabbered. When the LAN8670/1/2 detects a remote transmit jabber error occurred on a remote device, the Remote Jabber Count (RMTJABCNT) field in the 10BASE‑T1S PCS Diagnostic 1 (T1SPCSDIAG1) register will be incremented. In addition, the End-of-Stream Error Delimiter (ESDERR) status bit in the Status 1 (STS1) register will set. If enabled by clearing the End-of-Stream Error Delimiter Mask (ESDERRM) bit in the Interrupt Mask 1 (IMSK1) register, the IRQ_N pin will assert when a remote jabber condition has been detected.