DS110RT410_15 Datasheet, PDF (16/60 Pages) Texas Instruments – Low-Power Multi-Rate Quad Channel Retimer

DS110RT410
SNLS460A – MAY 2013 – REVISED OCTOBER 2015
www.ti.com
The SMBus is a standard communications bus for configuring simple systems. For a specification of the SMBus
and description of its operation, see smbus.org/specs/.
7.4.4 Standards-Based Modes
The DS110RT410 is designed to automatically operate with various multi-band data standards.
The first set of register writes constrain the coarse VCO tuning and the VCO divider ratios. When these registers
are set as indicated in Table 2, the DS110RT410 restricts its coarse VCO tuning to a set of coarse tuning values.
It also restricts the VCO divider ratio to the set of divider ratios required to cover the frequency bands for the
desired data rate standard. This enables the DS110RT410 to acquire phase lock more quickly than would be
possible if the coarse tuning range were unrestricted.
STANDARDS
Ethernet
Fibre-Channel
Infiniband
SDH/SONET
PROP1a
PROP1b
Interlaken 2
SFF-8431
Table 2. Standards-Based Modes Register Settings
DATA RATES (Gbps)
1.25, 10.3125
2.125, 4.25, 8.5, 10.51875
2.5, 5, 10
2.48832, 9.95328
8.25
8.5
10.3125
9.95328
VCO FREQUENCIES
(GHz)
10.0, 10.3125
8.5, 10.51875
10.0
9.5328
8.25
8.5
10.3125
9.95328
DIVIDER RATIOS
1, 8
1, 2, 4
1, 2, 4
1, 4
1
1
1
1
REGISTER 0x2F VALUE
(hex)
0x06
0x16
0x26
0x56
0x76
0x86
0xC6
0xD6
As an example of the usage of the registers in Table 2, assume that the retimer is required to operate in 10-GbE
or 1-GbE mode. By setting register 0x2f, bits 7:4, to 4'b0000, the DS110RT410 will automatically set its divider
ratio and its coarse VCO tuning setting to lock to either a 10-GbE signal (at 10.3125 Gbps) or a 1-GbE signal (at
1.25 Gbps) at its input.
For Fibre-Channel, the standard requiring a 10.51875-GHz VCO frequency and the standard requiring an
8.5-GHz VCO frequency require different settings for the registers listed in Table 2. The retimer cannot
automatically switch between these two standards.
For some standards listed in Table 2, the required VCO frequency is the same for each data rate in the standard.
Only the divider ratios are different. The retimer can automatically switch between the required divider ratios with
a single set of register settings.
For other data rates, it is also necessary to set the expected PPM count and the PPM count tolerance. These are
the values the retimer uses to detect a valid frequency lock.
For the 10-GbE and 1-GbE mode listed in Table 2, two frequency groups are defined. These two frequency
groups are referred to as Group 0, for 1 GbE, and Group 1, for 10 GbE. This same frequency group structure is
present for all frequency modes, but for some modes the expected frequency for both groups is the same. The
expected PPM count information for Group 0 is set in registers 0x60 and 0x61. For Group 1, it is set in registers
0x62 and 0x63. For both groups, the PPM count tolerance is set in register 0x64.
The value of the PPM count for either group is computed the same way from the expected data rate in Gbps,
R_Gbps. The PPM count value, denoted N_PPM, is computed by N_PPM = R_Gbps × 1280.
As an example we consider the PPM count setup for 10 GbE and 1 GbE. The expected PPM count for Group 0,
which in this case is 1 GbE, is set in registers 0x60 and 0x61. The expected VCO frequency for 1 GbE is
10.0 GHz. The actual data rate for 1 GbE, which is 8B/10B coded, is 1.25 Gbps. With a VCO divide ratio of 8,
which is the divide ratio automatically used by the retimer for 1 GbE, this yields a VCO frequency of 10.0 GHz.
We compute the PPM count as N_PPM = 10.0 × 1280 = 12800. This is a decimal value. In hexadecimal, this is
0x3200.
The lower-order byte is loaded into register 0x60. The higher order byte, 0x32, is loaded into the 7 least-
significant bits of register 0x61. In addition, bit 7 of register 0x61 is set, indicating manual load of the PPM count.
When this is complete, register 0x60 will contain 0x00. Register 0x61 will contain 0xb2.
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