Using PEX 8648 SMA Based (SI) Card White Paper – Version 1.3
© 2010 by PLX Technology, Inc. All Rights Reserved
6
4 Appendix
4.1 Obtaining a Gen 2 Compliance pattern for Observation
This can be done with I
2
C or In-band command (In-Band provided Port 3 is not upstream Port)
1. Connect the desired SMA TX lane to the high speed scope – the internal 50
Ω
termination of the
scope is required for the circuit to operate.
2. With the PLX SDK active, open the memory mapped register set. (left side of screen)
3. Go to register 0234h bits 19:16 (Disable Port X). Set bits 19:16 to “8”. (disables Port 3)
4.
Go to register 3098h (Link Status and Control). Set bit 4=1. (Enter Compliance).
Note: bits 3:0 should already have a register value of “2”
5. Go to register 0234h. Return bits 19:16 to “0”.
Terminated link is now in Gen 2 Compliance mode.
If it is desired to change the TX swing and emphasis settings, it can be done as below without resetting
the chip.
1. Go to register 0B90 (SerDes Drive Level 3) –
Depress a register read.
Value returned should
be the default Gen 2 value of “0E”.
2. Go to register 0BA0 (SerDes Post Cursor Emp) -
Depress a register read.
Value returned
should be the default Gen 2 value of “15”
3. With the Gen 2 values confirmed, you can now change these settings in accordance with the
formula outlined in the
PEX 8648 Data Book
for Swing and Pre-emphasis (Table 19-10 thru 19-
12) Swing setting is loosely approximated as 20log ((Drive + De-emp)/(Drive – De-emp))
As a point of note, we have observed some ‘bit flips’ when using I
2
C for changing these registers. To
confirm final setting, be sure to read back value after adjustment. Need to confirm against SDK SW
revisions.
