ENC28J60
When an enabled interrupt occurs, the interrupt pin will
remain low until all flags which are causing the interrupt
are cleared or masked off (enable bit is cleared) by the
host controller. If more than one interrupt source is
enabled, the host controller must poll each flag in the
EIR register to determine the source(s) of the interrupt.
It is recommended that the Bit Field Clear (BFC) SPI
command be used to reset the flag bits in the EIR reg-
ister rather than the normal Write Control Register
(WCR) command. This is necessary to prevent unin-
tentionally altering a flag that changes during the write
command. The BFC and WCR commands are dis-
cussed in detail in Section 4.0 “Serial Peripheral
Interface (SPI)”.
12.0 INTERRUPTS
The ENC28J60 has multiple interrupt sources and an
interrupt output pin to signal the occurrence of events
to the host controller. The interrupt pin is designed for
use by a host controller that is capable of detecting fall-
ing edges.
Interrupts are managed with two registers. The EIE
register contains the individual interrupt enable bits for
each interrupt source, while the EIR register contains
the corresponding interrupt flag bits. When an interrupt
occurs, the interrupt flag is set. If the interrupt is
enabled in the EIE register and the INTIE global inter-
rupt enable bit is set, the INT pin will be driven low (see
Figure 12-1).
After an interrupt occurs, the host controller should
clear the global enable bit for the interrupt pin before
servicing the interrupt. Clearing the enable bit will
cause the interrupt pin to return to the non-asserted
state (high). Doing so will prevent the host controller
from missing a falling edge should another interrupt
occur while the immediate interrupt is being serviced.
After the interrupt has been serviced, the global enable
bit may be restored. If an interrupt event occurred while
the previous interrupt was being processed, the act of
resetting the global enable bit will cause a new falling
edge on the interrupt pin to occur.
Note:
Except for the LINKIF interrupt flag,
interrupt flag bits are set when an interrupt
condition occurs regardless of the state of
its corresponding enable bit or the associ-
ated global enable bit. User software
should ensure the appropriate interrupt flag
bits are clear prior to enabling an interrupt.
This feature allows for software polling.
FIGURE 12-1:
ENC28J60 INTERRUPT LOGIC
PKTIF
PKTIE
DMAIF
PLNKIF
PLNKIE
DMAIE
PGIF
LINKIF
INT
PGEIE
LINKIE
TXIF
INT
TXIE
INTIE
TXERIF
TXERIE
RXERIF
RXERIE
© 2006 Microchip Technology Inc.
Preliminary
DS39662B-page 63
MICROCHIP [ MICROCHIP ]
