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CHAPTER 4 INTERFACES
104
(b) Cell-level handshaking mode
The signal timing in cell-level handshaking mode is the same as that in octet-level handshaking mode,
except that the EMPTY_B signal is replaced by the RCLAV signal. The RCLAV signal is used by the
PHY device to indicate whether there is subsequent cell data to be transmitted. When there is no more
cell data, the PHY device drives the RCLAV signal low in the next cycle of the last octet of the cell data
currently being transferred. The
μ
PD98405 does not load the data on Rx7 through Rx0 in a cycle in
which the RCLAV signal is low. The input timing of the RCLAV signal is the same as that for the
EMPTY_B signal in octet-level handshaking mode.
Figure 4-33. Receive Timing in Cell-Level Handshaking Mode
RSOC
Rx7-Rx0
RxCLAV
RENBL_B
RCLK
61
60
59
58
9
8
7
6
5
4
3
2
1
H4
H3
X
H2
H1
P48
P47
X
P48
P47
P46
Remark
H: ATM cell header P: ATM cell payload X: Invalid
(3) External receive FIFO use mode
Even when using an internal PHY layer, an external receive FIFO can be connected to the
μ
PD98405 via a
UTOPIA interface. When the PHM bit of the GMR register is 0 (the internal PHY layer is used) and the
EFM bit is 1, the
μ
PD98405 transmits the data, received at the internal PHY layer, from the transmission
side of the UTOPIA interface in sync with the internal TCLK. In this case, the UTOPIA interface operates in
an octet level handshake manner; the transmission side transmits the PHY layer data and the reception
side receives the SAR layer data. The UTOPIA interface operates according to the SAR layer UTOPIA
signal and timing. See
Section 4.3.1
for details of the UTOPIA interface signal timings. The block diagram
of an external receive FIFO connection is shown below.