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CHAPTER 3 FUNCTIONAL DESCRIPTION
User’s Manual S14054EJ4V0UM
36
In the 32-bit dual bus mode, writing data to the transmit FIFO is enabled by making the TXFEN# signal low. In
the 64-bit single bus mode, the FEN# and FRW signals are made low.
When these signals are asserted, the TXFBAn signal function of all the ports is enabled. Each port makes the
TXFBAn signal high if the data stored in the transmit FIFO does not exceed the value set by the TFDMH field of
the TFIC register. In this way, the host system can recognize that a quantity of free space set in advance is
available in the transmit FIFO for each port.
When the high level of the TXFBAn signal is recognized, the host system starts writing transmit data. The host
system prepares necessary data on TXFPT[2:0], TXFD[31:0], and TXFDQ[3:0] in the 32-bit dual bus mode, and
on TXFPT[2:0], FD[63:0], and FDQ[3:0] in the 64-bit single bus mode.
TXFPT[2:0] are signals that specify the port number of the port that transmits packets. The host system gives
the port number of the transmit FIFO to which it will write data, to these pins. TXFD[31:0] and FD[63:0] are the
data buses through which data is written to the transmit FIFO in the respective bus modes. TXFDQ[3:0] and
FDQ[3:0] are signals indicating the attribute of the data on the FIFO data bus, and input the attribute of the data
on TXFD[31:0] or FD[64:0] in each bus mode of the host system.
The attributes of data include idle, data start, intermediate, and data end. If end data includes a fraction, this
data attribute informs the
µ
PD98431 that fraction processing is necessary. In addition, automatic appending of a
CRC code can be also instructed by setting an attribute. Tables 3-1 and 3-2 show the relations between
TXFDQ[3:0] and FDQ[3:0] inputs, and data attributes.
Table 3-1. TXFDQ Pins and Transmit Data Attributes (32-Bit Dual Bus)
TXFDQ pins
Data Attribute
Valid Data Byte Position
[3]
[2]
[1]
[0]
Little Endian
Big Endian
0
0
0
0
Idle
–
–
0
0
0
1
Data start
TXFD[31:0]
TXFD[31:0]
0
0
1
0
Intermediate data
TXFD[31:0]
TXFD[31:0]
0
0
1
1
Data start (with CRC appended)
TXFD[31:0]
TXFD[31:0]
0
1
×
×
Reserved
–
–
1
0
0
0
Data end 0
TXFD[31:0]
TXFD[31:0]
1
0
0
1
Data end 1
TXFD[7:0]
TXFD[31:24]
1
0
1
0
Data end 2
TXFD[15:0]
TXFD[31:16]
1
0
1
1
Data end 3
TXFD[23:0]
TXFD[31:8]
1
1
×
×
Reserved
–
–
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