DS125RT410 Datasheet, PDF (34/42 Pages) Texas Instruments – DS125RT410 Low Power Multi-Rate Quad Channel Retimer

DS125RT410
SNLS459 – APRIL 2011
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Register 0x31, bits 4:3
0x3
Table 12. Figure of Merit Type Setting (continued)
Figure of Merit Type
Both HEO and VEO are used (default)
For some transmission media the adaptation can reach a better setting if a different figure of merit is used. The
DS125RT410 includes the capability of adapting based on a configurable figure of merit. The configurable figure
of merit is structured as shown in the equation below.
FOM = (HEO – b) X a + (VEO – c) x (1 – a)
In this equation, HEO is horizontal eye opening, VEO is vertical eye opening, FOM is the figure of merit, and the
factors a, b, and c are set using registers 0x6b, 0x6c, and 0x6d respectively.
In order to use the configurable figure of merit, the enable bits must be set. To use the configurable figure of
merit for the CTLE adaptation, set bit 7 of register 0x6e, the en_new_fom_ctle bit.
Setting the Rate and Subrate for Lock Acquisition
Register 0x2f, bits 7:6 and 5:4
The rate and subrate settings, which constrain the data rate search in order to reduce lock time, can be set using
channel register 0x2f. Bits 7:6 are RATE<1:0>, and bits 5:4 are SUBRATE<1:0>. These four bits form a hex digit
which matches the codes in Table 1.
Setting the Adaptation/Lock Mode
Register 0x31, bits 6:5, Register 0x3e, bit 7, and Register 0x6a
There are 2 adaptation modes available in the DS125RT410.
• Mode 0: The user is responsible for setting the CTLE values. This mode is used if the transmission channel
response is fixed.
• Mode 1: Only the CTLE is adapted to equalize the transmission channel. This mode is primarily used for
smoothly-varying high-loss transmission channels such as cables and simple PCB traces.
Bits 6:5 of register 0x31 determine the adaptation mode to be used. The mapping of these register bits to the
adaptation algorithm is shown in Table 13.
Register 0x31, Bit 6
adapt_mode[1]
0
0
Table 13. DS125RT410 Adaptation Algorithm Settings
Register 0x31, Bit 5
adapt_mode[0]
0
1
Adapt Mode Setting <1:0>
00
01
Adaptation Algorithm
No Adaptation
Adapt CTLE Until Optimum
(Default)
By default the DS125RT410 requires that the equalized internal eye exhibit horizontal and vertical eye openings
greater than a pre-set minimum in order to declare a successful lock. The minimum values are set in register
0x6a.
The DS125RT410 continuously monitors the horizontal and vertical eye openings while it is in lock. If the eye
opening falls below the threshold set in register 0x6a, the DS125RT410 will declare a loss of lock.
Initiating Adaptation
Register 0x24, bit 2, and Register 0x2f, bit 0
When the DS125RT410 becomes unlocked, it will automatically try to acquire lock. If an adaptation mode is
selected using bits 6:5 in register 0x31, the DS125RT410 will also try to adapt its CTLE.
Adaptation can also be initiated by the user. CTLE adaptation can be initiated by setting and then clearing
register 0x2f, bit 0.
Setting the Reference Enable Mode
Register 0x36, bits 5:4
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