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CHAPTER 3 FUNCTIONAL DESCRIPTION
User’s Manual S14054EJ4V0UM
54
(3) Interrupt servicing
If an interrupt occurs, the
µ
PD98431 makes the INT# signal low to report to the host system. The sources of
interrupts are as follows:
•
Transmit packet status information indicated by TSVREG1 register
•
Receive packet status information indicated by RSVREG register
•
FIFO status information indicated in FSVREG register
•
Overflow of statistics counter indicated by CAR1 and CAR2 registers
After the INT# signal has been asserted, the host system can check at which port the interrupt has occurred and
by which status source the INT# signal has been asserted, by reading the STIR register. By reading the status
register of the corresponding port, the host system can identify the interrupt source in detail.
If an interrupt source that asserts the INT# signal is generated in the status register provided for each port, the
corresponding bit of the STIR register is set to 1. Even if the STIR register has been read, neither the status
register nor the INT# signal is cleared.
An interrupt mask can be specified for each interrupt source. If an interrupt is caused by a masked source, the
corresponding bit of each status register is set to 1. However, the INT# signal is not asserted, nor is the
corresponding bit of the STIR register set to 1.
Each status register is automatically cleared when it is read while the SRRC bit of the MISCR register is set to 1.
The INT# signal is deasserted when the status registers of all the ports (except the masked bits) have been
cleared.
3.8 Network Interface
The
µ
PD98431 has an MII (Media Independent Interface) and a 10 Mbps serial interface to interface the network.
The interface to be used can be selected for each port by using the EXINT bit of the PCSC register.
3.8.1 MII (Media Independent Interface)
The MII is an interface defined by IEEE802.3u. This interface transmits or receives data independently of the
media type (STP, UTP, or optical fiber) and transfer rate (10 Mbps or 100 Mbps). This interface has a data bus 4 bits
(nibble) wide to transmit or receive data, and control signals. In addition, a two-wire serial interface and an MII
management interface are also provided to implement access between the
µ
PD98431 and PHY device by using the
MII management frame.
The
µ
PD98431 supports transmission/reception, nibble data bus, and control signals for each port. It is provided
with one MII management interface port.
3.8.2 MII management interface
(1) MDC clock
The
µ
PD98431 generates the MDC clock used for the MII management interface by dividing the clock input to
the HCLK pin. To conform with the IEEE standard, the division ratio must be set in accordance with the HCLK
input. The division ratio is set by the CLKS bit of the MIIC register. Table 3-5 shows the relation between the
HCLK input and CLKS bit.
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