
MPC8533E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 6
62
Freescale Semiconductor
High-Speed Serial Interfaces (HSSI)
requirement for average voltage (common mode voltage) to be between 100 and 400 mV.
Figure 42 shows the SerDes reference clock input requirement for DC-coupled connection
scheme.
— For external AC-coupled connection, there is no common mode voltage requirement for the
clock driver. Since the external AC-coupling capacitor blocks the DC level, the clock driver
and the SerDes reference clock receiver operate in different command mode voltages. The
SerDes reference clock receiver in this connection scheme has its common mode voltage set to
SGND_SRDSn. Each signal wire of the differential inputs is allowed to swing below and above
the command mode voltage (SGND_SRDSn).
Figure 43 shows the SerDes reference clock
input requirement for AC-coupled connection scheme.
Single-ended Mode
— The reference clock can also be single-ended. The SDn_REF_CLK input amplitude
(single-ended swing) must be between 400 and 800 mV peak-peak (from Vmin to Vmax) with
SDn_REF_CLK either left unconnected or tied to ground.
—The SDn_REF_CLK input average voltage must be between 200 and 400 mV.
Figure 44 shows
the SerDes reference clock input requirement for single-ended signaling mode.
— To meet the input amplitude requirement, the reference clock inputs might need to be DC or
AC-coupled externally. For the best noise performance, the reference of the clock could be DC
or AC-coupled into the unused phase (SDn_REF_CLK) through the same source impedance as
the clock input (SDn_REF_CLK) in use.
Figure 42. Differential Reference Clock Input DC Requirements (External DC-Coupled)
Figure 43. Differential Reference Clock Input DC Requirements (External AC-Coupled)
SDn_REF_CLK
Vmax < 800 mV
Vmin > 0 V
100 mV < Vcm < 400 mV
200 mV < Input Amplitude or Differential Peak < 800 mV
SDn_REF_CLK
Vcm
200 mV < Input Amplitude or Differential Peak < 800 mV
Vmax < Vcm + 400 mV
Vmin > Vcm - 400 mV