Abstract: With the addition of network protection components and/or the need to route signals through connectors and other PC board requirements, sometimes it is necessary to manipulate the transmit waveform. The DS26528 and DS26524 contain precise methods for making minor or major changes to the output pulse. This application note provides the information required to access factory test registers that allow the transmit waveform to be modified to meet a wide variety of application requirements.
T1 and E1 Transmit Waveform Programmable Sections
The DS26528 and DS26524 contain registers that provide control for the transmit pulse in two major areas: amplitude and timing. T1 and E1 transmit pulses are divided into sections, each of which may be manipulated to provide the desired waveform. Figure 1 shows how the T1 pulse is divided and the registers that control each section. Figure 2 provides the same information for the E1 pulse.
T1 and E1 Transmit Waveform Amplitude Control
The amplitude of the DS26528 and DS26524 transmit pulse may be controlled in two ways:
Adjusting the DAC Gain
The L1TXLAE register bits DAC[3:0] provide positive and negative adjustment of all the T1 or E1 levels simultaneously.
Partial Waveform Level Adjustment
The WLA[3:0] bits of the Level Adjustment registers provide fine tuning of specific sections of the waveform. The step size of the voltage level will change in proportion to the programmed DAC gain. If the DAC gain is increased by 10%, then the step sizes will also increase by 10%.
T1 and E1 Transmit Waveform Timing Control
The timing of the DS26528 and DS26524 transmit pulse levels are controlled by the CEA[2:0] bits of the Level Adjustment registers. Each edge may be moved in both positive and negative directions in increments of 1/32 of TCLK.
General Recommendations
Modifying the DAC gain is the easiest method of controlling the amplitude of the transmit pulse, because it will control the entire waveform with only one register change. Using the DAC gain first will allow for minimal, if any, modifications of the individual Level Adjustment registers.
The maximum output of the DAC will be affected by VDD. At lower levels of VDD, the maximum DAC gain setting may be unattainable. Changing VDD will also affect the maximum voltage attainable by the line driver's output stage.
Negative values do not use signed integer representation. The MSB is the sign bit and the LSBs represent magnitude irrespective of sign. For example, a -3 in a WLA[3:0] register would be 1011b (bit 3 set to 1 means negative, 011 in the next 3 bits is magnitude 3), not 1101b (4-bit signed integer representation).
Figure 1. T1 Pulse control sections.
T1 Pulse Control Sections
Overshoot (1) -- Register L1TXLAA WLA[4:0]
Clock Edge (1CE) -- Register L1TXLAA CEA[2:0]
(1CE) = Clock Edge transition from Overshoot to Plateau
Plateau (2) -- Register L1TXLAB WLA[4:0]
Clock Edge (2CE) -- Register L1TXLAB CEA[2:0]
(2CE) = Clock Edge transition from Plateau to Falling Edge
Undershoot (3) -- Register L1TXLAC WLA[4:0]
Clock Edge (3CE) -- Register L1TXLAC CEA[2:0]
(3CE) = Clock Edge transition from Falling Edge to End of Undershoot (3)
Undershoot (4) -- Register L1TXLAD WLA[4:0]
Clock Edge (4CE) -- Register L1TXLAD CEA[2:0]
(4CE) = Clock Edge transition from End of Undershoot (3) to End of Undershoot (4)
Undershoot (5) -- Register L1TXLAC WLA[4:0]
Figure 2. E1 Pulse control sections.
E1 Pulse Control Sections
Overshoot (1) -- Register L1TXLAA WLA[4:0]
Clock Edge (1CE) -- Register L1TXLAA CEA[2:0]
(1CE) = Clock Edge transition from Overshoot to Plateau
Plateau (2) -- Register L1TXLAB WLA[4:0]
Clock Edge (2CE) -- Register L1TXLAB CEA[2:0]
(2CE) = Clock Edge transition from Plateau to Falling Edge
NOTE:
Registers L1TXAC, L1TXAD, and L1TXAE are not used in E1 mode.
LIU Test Register Descriptions for the DS26528 and DS26524
Table 1 provides the register address and description for LIU 1. These registers are duplicated for LIUs 2 through 8. Table 2 provides the addresses for all of the LIU test registers. The DS26524 does not contain LIU 5 through 8.
Table 1. LIU 1 Test Registers
Address
Abbr
Description
1008h
L1TXLAA
LIU 1 Tx Level Adjust A (Test Register)
1009h
L1TXLAB
LIU 1 Tx Level Adjust B (Test Register)
100Ah
L1TXLAC
LIU 1 Tx Level Adjust C (Test Register)
100Bh
L1TXLAD
LIU 1 Tx Level Adjust D (Test Register)
100Ch
L1TXLAE
LIU 1 Tx Level Adjust E (Test Register)
Table 2. LIU Test Register Address Range
LIU
Address Range
1
1008 - 100Ch
2
1028 - 102Ch
3
1048 - 104Ch
4
1068 - 106Ch
DS26528 Only
5
1080 - 108Ch
6
10A8 - 10ACh
7
10C8 - 10DCh
8
10E8 - 10ECh
Detailed LIU Test Register Documentation
The following provides the register address and description for LIU 1. These registers are duplicated for LIUs 2 through 8. See Table 2 for the addresses for all of the LIU test registers.
Register Name:
L1TXLAA
Register Description:
LIU Tx Level Adjust A (Overshoot Voltage)
Register Address:
1008H
Read/Write Function:
R/W
Bit #
7
6
5
4
3
2
1
0
Name
WLA4
WLA3
WLA2
WLA1
WLA0
CEA2
CEA1
CEA0
Default
0
0
0
0
0
0
0
0
Bits 7 to 3: Transmit Waveform Levels Adjust for Output Level 1 (WLA[4:0]). Moves magnitude from default ±360mV.
Bit 7 = sign bit ('1' means negative)
Bits 6 to 3 = magnitude (unsigned)
i.e., 24mV is LSB step size
Bits 2 to 0: Clock Edge Adjust (CEA[2:0]). Moves clock edge ±3 32x-clks from default.
<2> = sign bit ('1' means negative)
<1:0> = number of 32x-clks to move (unsigned)
Register Name:
L1TXLAB
Register Description:
LIU Tx Level Adjust B (Plateau Voltage)
Register Address:
1009H
Read/Write Function:
R/W
Bit #
7
6
5
4
3
2
1
0
Name
WLA4
WLA3
WLA2
WLA1
WLA0
CEA2
CEA1
CEA0
Default
0
0
0
0
0
0
0
0
Bits 7 to 3: Transmit Waveform Levels Adjust for Output Level 2 (WLA[4:0]). Moves magnitude from default ±360mV.
Bit 7 = sign bit ('1' means negative)
Bits 6 to 3 = magnitude (unsigned)
i.e., 24mV is LSB step size
Bits 2 to 0: Clock Edge Adjust (CEA[2:0]). Moves clock edge ±3 32x-clks from default.
<2> = sign bit ('1' means negative)
<1:0> = number of 32x-clks to move (unsigned)
Register Name:
L1TXLAC
Register Description:
LIU Tx Level Adjust C (Undershoot Voltage #1)
Register Address:
100AH
Read/Write Function:
R/W
Bit #
7
6
5
4
3
2
1
0
Name
WLA4
WLA3
WLA2
WLA1
WLA0
CEA2
CEA1
CEA0
Default
0
0
0
0
0
0
0
0
Bits 7 to 3: Transmit Waveform Levels Adjust for Output Level 3 (WLA[4:0]). Moves magnitude from default ±360mV.
Bit 7 = sign bit ('1' means negative)
Bits 6 to 3 = magnitude (unsigned)
i.e., 24mV is LSB step size
Bits 2 to 0: Clock Edge Adjust (CEA[2:0]). Moves clock edge ±3 32x-clks from default.
<2> = sign bit ('1' means negative)
<1:0> = number of 32x-clks to move (unsigned)
Register Name:
L1TXLAD
Register Description:
LIU Tx Level Adjust D (Undershoot Voltage #2)
Register Address:
100BH
Read/Write Function:
R/W
Bit #
7
6
5
4
3
2
1
0
Name
WLA4
WLA3
WLA2
WLA1
WLA0
CEA2
CEA1
CEA0
Default
0
0
0
0
0
0
0
0
Bits 7 to 3: Transmit Waveform Levels Adjust for Output Level 4 (WLA[4:0]). Moves magnitude from default ±360mV.
Bit 7 = sign bit ('1' means negative)
Bits 6 to 3 = magnitude (unsigned)
i.e., 24mV is LSB step size
Bits 2 to 0: Clock Edge Adjust (CEA[2:0]). Moves clock edge ±3 32x-clks from default.
<2> = sign bit ('1' means negative)
<1:0> = number of 32x-clks to move (unsigned)
Register Name:
L1TXLAE
Register Description:
LIU Tx Level Adjust E (Undershoot Voltage #3)
Register Address:
100CH
Read/Write Function:
R/W
Bit #
7
6
5
4
3
2
1
0
Name
WLA4
WLA3
WLA2
WLA1
WLA0
CEA2
CEA1
CEA0
Default
0
0
0
0
0
0
0
0
Bits 7 to 4: Transmit Waveform Levels Adjust for Output Level 5 (WLA[3:0]). Moves magnitude from default ±180mV.
Bit 7 = sign bit ('1' means negative)
Bits 6 to 4 = magnitude (unsigned)
i.e., 24mV is LSB step size
Bits 3 to 0: DAC Gain Adjust (DAC[3:0]). The following settings change the gain of the DAC.
0000 - nominal DAC gain (default)
0001 - DAC gain +2.6%
0010 - DAC gain +5.3%
0011 - DAC gain +8%
0100 - DAC gain +11.1%
0101 - DAC gain +14.2%
0110 - DAC gain +17.7%
0111 - DAC gain +21.3%
1000 - DAC gain -2.2%
1001 - DAC gain -4.88%
1010 - DAC gain -7.11%
1011 - DAC gain -8.88%
1100 - DAC gain -11.11%
1101 - DAC gain -12%
1110 - DAC gain -15.1%
1111 - DAC gain -16.4%
T1 and E1 Transmit Waveform Data
The following data is representative of the expected results for both the DS26528 and DS26524. The data is provided as a guideline for determining the range and method of using the Level Adjustment registers for controlling the amplitude and timing of the T1 and E1 transmit pulses. The data was taken at room temperature with 3.3V VDD.
DS26528 and DS26524 Information
For more information about Dallas Semiconductor's products, please consult the data sheets available on our website at www.maxim-ic.com/telecom. If you have further questions concerning the operation of Maxim/Dallas devices, please contact the Telecommunication Applications support team by email at or call 972-371-6555.
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