2–32
Altera Corporation
Stratix II GX Device Handbook, Volume 2
October 2007
Transmitter Modules
The transmitter phase compensation FIFO buffer is always used and
cannot be bypassed. The input to the transmitter phase compensation
FIFO buffer is the data from the PLD logic array or the PIPE interface in
PIPE mode.
Transmitter Phase Compensation FIFO Error Flag
The write port of the transmitter phase compensation FIFO can be
clocked by either transmitter PLL output clock (
tx_clkout
or
coreclkout
) or a PLD clock. The read port is always clocked by the
transmitter PLL output clock. In all configurations, the write clock and
the read clock must have 0 PPM difference to avoid overrun/underflow
of the phase compensation FIFO.
An optional
debug_tx_phase_comp_fifo_error
port is available in
all modes to indicate transmitter phase compensation FIFO
overrun/underflow condition. The
debug_tx_phase_comp_fifo_error
is asserted high when the phase
compensation FIFO gets either full or empty. This feature is useful to
verify the phase compensation FIFO overrun/underflow condition as a
probable cause of link errors.
Byte Serializer
The byte serializer (
Figure 2–23
) converts the two- or four-byte interface
into a one- or two-byte-wide data path for the transceiver from the PLD
interface. The PLD interface has a limit of 250 MHz, so the byte serializer
is required to stripe the parallel data into the single- or double-wide
transceiver data path. At 6.375 Gbps, the transceiver logic has a
double-byte-wide data path that runs at 318.75 MHz in a ×20 serializer
factor, which is above the maximum PLD interface speed. By using the
byte serializer, the PLD interface width doubles to 40-bits (36 bits when
using the 8B/10B encoder) and the interface speed drops to 159.375 MHz.
Figure 2–23. Byte Serializer
Byte Serializer
dataout[19..0]
From Transmitter
Phase
Compensation
FIFO
datain[39..0]
Control Signals in [3..0]
Control Signals out [1..0]
To 8B/10B Encoder
Slow-Speed
Transmitter Clock
Slow-Speed
Transmitter Clock
or Divide by 2 Version
÷
2