80 lines
5.6 KiB
Markdown
80 lines
5.6 KiB
Markdown
# Broadcom Tri-Mode SerDes to SFF-TA-1016 (MCIO 8i) Breakout Architecture
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**System:** 6U 19-Inch Open-Source Tri-Mode Storage Array
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**Document ID:** ELEC-SPEC-03
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**Storage Silicon:** Broadcom SAS3408 (8-PHY) / SAS3416 (16-PHY) Tri-Mode IOC
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**Connector Standard:** SFF-TA-1016 (Mini Cool Edge IO / MCIO 8i, 74-Pin Surface Mount)
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**Cable Interconnect:** 85Ω / 100Ω Low-Loss Twinaxial Copper Ribbon Harness (Amphenol / Molex / JPC)
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---
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## 1. SerDes Offloading & SI Architecture
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Routing 12 Gbps SAS and 8 GT/s PCIe signals across long distances on a budget 4-layer FR4 baseboard causes severe high-frequency dielectric attenuation. By terminating the Broadcom SerDes outputs immediately ($< 25.0\,\text{mm}$ trace distance) into SFF-TA-1016 surface-mount MCIO connectors, signals transition into shielded twinaxial copper lines, eliminating the need for expensive high-layer Megtron/Rogers substrates.
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```
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[Broadcom SAS3408] ───< 25mm 4-Layer FR4 ───► [MCIO 8i SFF-TA-1016]
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(8 Tri-Mode PHYs) (74-Pin High-Density Receptacle)
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│
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▼
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[Passive 8-Bay U.3 Backplane] ◄── Twinax Ribbon Cable ──┘
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(SFF-TA-1001 Universal Bays) (Loss < 0.15 dB/inch @ 6 GHz)
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```
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---
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## 2. Complete MCIO 8i (74-Pin) Pinout & Signal Mapping
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Connector Reference: `J_MCIO1` (Amphenol `G88MP08102CEEU` or Molex `2150711403`).
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| Pin | Side A Signal | Broadcom Net / Source | Pin | Side B Signal | Broadcom Net / Source |
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| :---: | :--- | :--- | :---: | :--- | :--- |
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| **A1** | **GND** | Board Solid Ground | **B1** | **GND** | Board Solid Ground |
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| **A2** | **RX0_P** | Broadcom PHY0_RX_P | **B2** | **TX0_P** | Broadcom PHY0_TX_P |
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| **A3** | **RX0_N** | Broadcom PHY0_RX_N | **B3** | **TX0_N** | Broadcom PHY0_TX_N |
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| **A4** | **GND** | Board Solid Ground | **B4** | **GND** | Board Solid Ground |
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| **A5** | **RX1_P** | Broadcom PHY1_RX_P | **B5** | **TX1_P** | Broadcom PHY1_TX_P |
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| **A6** | **RX1_N** | Broadcom PHY1_RX_N | **B6** | **TX1_N** | Broadcom PHY1_TX_N |
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| **A7** | **GND** | Board Solid Ground | **B7** | **GND** | Board Solid Ground |
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| **A8** | **RX2_P** | Broadcom PHY2_RX_P | **B8** | **TX2_P** | Broadcom PHY2_TX_P |
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| **A9** | **RX2_N** | Broadcom PHY2_RX_N | **B9** | **TX2_N** | Broadcom PHY2_TX_N |
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| **A10**| **GND** | Board Solid Ground | **B10**| **GND** | Board Solid Ground |
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| **A11**| **RX3_P** | Broadcom PHY3_RX_P | **B11**| **TX3_P** | Broadcom PHY3_TX_P |
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| **A12**| **RX3_N** | Broadcom PHY3_RX_N | **B12**| **TX3_N** | Broadcom PHY3_TX_N |
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| **A13**| **GND** | Board Solid Ground | **B13**| **GND** | Board Solid Ground |
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| **A14**| **SGPIO_SCLK** | SGPIO Clock (AA14) | **B14**| **UBM_I2C_SCL** | Universal Backplane I2C SCL |
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| **A15**| **SGPIO_SLOAD**| SGPIO Load (AA15) | **B15**| **UBM_I2C_SDA** | Universal Backplane I2C SDA |
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| **A16**| **SGPIO_SDOUT**| SGPIO Data Out (AB14) | **B16**| **BP_RST#** | Backplane Reset (Active Low) |
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| **A17**| **SGPIO_SDIN** | SGPIO Data In (AB15) | **B17**| **BP_INT#** | Backplane Interrupt Alert |
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| **A18**| **GND** | Board Solid Ground | **B18**| **GND** | Board Solid Ground |
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| **A19**| **RX4_P** | Broadcom PHY4_RX_P | **B19**| **TX4_P** | Broadcom PHY4_TX_P |
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| **A20**| **RX4_N** | Broadcom PHY4_RX_N | **B20**| **TX4_N** | Broadcom PHY4_TX_N |
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| **A21**| **GND** | Board Solid Ground | **B21**| **GND** | Board Solid Ground |
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| **A22**| **RX5_P** | Broadcom PHY5_RX_P | **B22**| **TX5_P** | Broadcom PHY5_TX_P |
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| **A23**| **RX5_N** | Broadcom PHY5_RX_N | **B23**| **TX5_N** | Broadcom PHY5_TX_N |
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| **A24**| **GND** | Board Solid Ground | **B24**| **GND** | Board Solid Ground |
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| **A25**| **RX6_P** | Broadcom PHY6_RX_P | **B25**| **TX6_P** | Broadcom PHY6_TX_P |
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| **A26**| **RX6_N** | Broadcom PHY6_RX_N | **B26**| **TX6_N** | Broadcom PHY6_TX_N |
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| **A27**| **GND** | Board Solid Ground | **B27**| **GND** | Board Solid Ground |
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| **A28**| **RX7_P** | Broadcom PHY7_RX_P | **B28**| **TX7_P** | Broadcom PHY7_TX_P |
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| **A29**| **RX7_N** | Broadcom PHY7_RX_N | **B29**| **TX7_N** | Broadcom PHY7_TX_N |
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| **A30**| **GND** | Board Solid Ground | **B30**| **GND** | Board Solid Ground |
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| **A31**| **3V3_AUX** | Standby +3.3V Power | **B31**| **3V3_AUX** | Standby +3.3V Power |
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| **A32**| **3V3_AUX** | Standby +3.3V Power | **B32**| **3V3_AUX** | Standby +3.3V Power |
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| **A33**| **GND** | Board Solid Ground | **B33**| **GND** | Board Solid Ground |
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| **A34**| **12V_SENSE** | Backplane 12V Rail Monitor | **B34**| **5V_SENSE** | Backplane 5V Rail Monitor |
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| **A35**| **GND** | Board Solid Ground | **B35**| **GND** | Board Solid Ground |
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| **A36**| **PRSNT0#** | Cable Presence Detect 0 | **B36**| **PRSNT1#** | Cable Presence Detect 1 |
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| **A37**| **GND** | Board Solid Ground | **B37**| **GND** | Board Solid Ground |
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---
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## 3. High-Speed Differential PCB Escape Routing
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1. **Symmetric Interstitial Shielding:** Ground pins are interleaved between every high-speed differential channel ($A_1, A_4, A_7, A_{10}, \dots$), achieving a Near-End Crosstalk (NEXT) isolation of $> -40\,\text{dB}$ across 0.1 to 10 GHz.
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2. **AC Coupling Capacitor Placement on SerDes TX:**
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- 100nF 0402 ceramic capacitors ($C_{201}$ to $C_{216}$) are placed in series on the Transmit differential tracks (`TX0_P/N` through `TX7_P/N`), located within $3.0\,\text{mm}$ of the MCIO connector pads.
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3. **Trace Length Matching on Carrier Board:**
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- Intra-pair skew (between P and N traces): Strictly matched to $< 2.0\,\text{mils}$ ($0.05\,\text{mm}$).
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- Inter-pair trace length variation: Matched to $< 25.0\,\text{mils}$ ($0.635\,\text{mm}$) across all 8 channels.
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