24888 Rev 3.03 - July 12, 2004 | |
Link PHY Compensation Control Registers | DevA:0x[E8, E4, E0] |
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The link PHY circuitry includes automatic compensation that is used to adjust the electrical characteristics for the link transmitters and receivers on both sides of the tunnel. There is one compensation circuit for the receiv- ers and one for each polarity of the transmitters. These registers provide visibility into the calculated output of the compensation circuits, the ability to override the calculated value with
•DevA:0xE0: transmitter rising edge (P) drive strength compensation.
•DevA:0xE4: transmitter falling edge (N) drive strength compensation.
•DevA:0xE8: receiver impedance compensation.
For DevA:0x[E4, E0], higher values represent higher drive strength; the values range from 01h to 13h (19 steps). For DevA:0xE8, higher values represent lower impedance; the values range from 00h to 1Fh (32 steps).
Note: the default state of these registers is set by PWROK reset; assertion of RESET# does not alter any of the fields.
Default: See below. | Attribute: See below. | |
Bits | Description |
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31 | Must be low. | |
| behavior. |
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30:21 | Reserved. |
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20:16 | CALCCOMP: calculated compensation value. Read only. This provides the calculated value from | |
| the auto compensation circuitry. The default value of this field is not predictable. | |
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15 | Reserved. |
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14:13 | BCTL: link side B PHY control value. | |
| compensation value that is applied to side B of the tunnel as follows: | |
| BCTL | Description |
| 00b | Apply CALCCOMP directly as the compensation value. |
| 01b | Apply BDATA directly as the compensation value. |
| 10b | Apply the sum of CALCCOMP and BDATA as the compensation value. In |
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| DevA:0x[E4, E0], if the sum exceeds 13h, then 13h is applied. In DevA:0x[E8], if the |
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| sum exceeds 1Fh, then 1Fh is applied. |
| 11b | Apply the difference of CALCCOMP minus BDATA as the compensation value. If the |
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| difference is less than 01h, then 01h is applied. |
| The default value of this field (from PWROK reset) is controlled by the CMPOVR signal. If | |
| CMPOVR = 0, the default is 00b. If CMPOVR = 1, the default is 01b. | |
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12:8 | BDATA: link side B data value. | |
| compensation as described in BCTL. The default for DevA:0x[E4, E0] is 08h. The default for | |
| DevA:0xE8 is 0Fh. | |
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7 | Reserved. |
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