3.3 INTERRUPT REGISTERS
When the MAC chip detects the occurrence of any of the following indication events, the
MAC sets the appropriate bit in the interrupt event register. This bit remains set until the
NP reads this register, which clears all bits. The MAC never clears these bits unless this
register is read. This register can be read by the NP at any time, but cannot be written by
the NP. The interrupt event register is cleared on power-up reset and is unaffected by a
MAC_RESET(other than some bits being set as a side effect).
When one of the bits in this register is one and the corresponding bit is set in the interrupt
mask register, the MACINT pin is asserted. This pin can be negated by either reading the
interrupt event register or by clearing the appropriate bits in the interrupt mask register.
When the receiver/transmitter FSMs are turned off (i.e., MAC_ON = 0), most events
described below cannot occur, although any previously marked event bits remain set until
the corresponding interrupt event register is read. The only event bits that can be set when
MAC_ON is zero are NP_ERR, SI_ERR, and PH_INVALID.
3.3.1 Interrupt Event Register A (INTR_EVENT_A)
PH_INVALID—PH_INVALID Indication Detected
This event is signaled when the ELM passes the MAC a PH_INVALID, indicating that
the PHY is in a line state other than active line state (ALS) or idle line state (ILS). When
the receiver FSM is operational, receipt of PH_INVALID causes the FSM to enter the
listen (R0) state.
U_TOKEN_RCVD—Unrestricted Token Received
This event is signaled when an unrestricted token is received (i.e., when the receiver
FSM signals JK_Received and R_Flag is cleared). The token is passed or captured by
the transmitter for this bit to be set. Also, RING_OPERATIONAL can be set or cleared
for this bit to be set.
R_TOKEN_RCVD—Restricted Token Received
This event is signaled when a restricted token is received (i.e., when the receiver FSM
signals JK_Received and R_Flag is set), regardless of whether the token is repeated or
captured by the transmitter. Also, RING_OPERATIONAL does not affect the setting of
MC68838 USER'S MANUAL