Am4 Pin Layout -

| Group | Pin Count (approx) | Primary Function | |-------|--------------------|------------------| | VDD (Core) | ~280 | CPU core power (1.1–1.5V) | | VDD_SOC | ~60 | Uncore (memory controller, infinity fabric) | | VDD_GFX (APU only) | ~90 | Integrated GPU power | | VDD_IO / VDD_18 | ~30 | 1.8V I/O (e.g., PLL, PCIe refclk) | | VDD_MEM (VDDIO_DDR) | ~40 | DDR4 memory interface power (1.2V) | | Ground (VSS) | ~350 | Return current & shielding | | PCIe lanes (16+4) | ~200 | PCIe Gen3/Gen4 (x16 GPU + x4 NVMe) | | DDR4 channels (2×64-bit) | ~150 | DDR4 data, address, command, clocks | | SATA / USB / GPIO | ~30 | Southbridge / FCH connection | | Control & straps | ~50 | RESET, PROCHOT, SMU, JTAG, strap config |

Abstract The AM4 socket, introduced by AMD in 2016, serves as the cornerstone for Ryzen processors (Zen, Zen+, Zen 2, Zen 3) and compatible APUs (Bristol Ridge, Raven Ridge, Cezanne). Unlike Intel’s LGA (Land Grid Array), AM4 uses a µPGA (Micro Pin Grid Array) with 1331 pins arranged in a 35×35 grid (with missing positions for keying). This paper provides a comprehensive breakdown of the pinout, including power delivery, PCIe, DDR4 memory channels, I/O (USB, SATA), and critical differences between CPU and APU configurations. 1. Introduction The AM4 socket unified AMD’s desktop platform for mainstream CPUs and APUs, replacing AM3+, FM2+, and AM1. Electrical compatibility depends not only on physical insertion but also on correct pin mapping, as some pins are reserved or repurposed between generations (e.g., X370 vs. X570 chipsets). Understanding the pin layout is essential for motherboard design, debugging, overclocking modifications, or diagnosing bent-pin failures. 2. Physical Layout Characteristics | Property | Specification | |----------|----------------| | Type | µPGA (Pin Grid Array) – pins on CPU | | Pin count | 1331 (arranged 35×35 with missing corners) | | Pin pitch | 1.0 mm | | Pin diameter | 0.45 mm (typical) | | Keying features | 3 corner cutouts (one pin missing in each corner except alignment corner) | | Socket mechanism | Zero Insertion Force (ZIF) lever arm | am4 pin layout

| Signal type | Example pins (CH_A) | Count | |-------------|---------------------|-------| | DQ [0..63] | DQ0–DQ63 (spread across rows) | 64 | | DQS (strobe) | DQS0_t/c, DQS1_t/c | 8 pairs | | CA (CMD/ADDR) | A0–A17, BA0–BA1, BG0–BG1 | ~25 | | CLK | MEMCLK_A_t/c, MEMCLK_B_t/c | 2 pairs | | VDD_MEM | Multiple pins | ~20 | | VREF_CA, VREF_DQ | Reference voltage pins | 2 | | Group | Pin Count (approx) | Primary

Complete 1331-pin maps are maintained by the community at resources like "AM4 V1.6 Pinout" (IOShield). AM5 (LGA1718) replaced AM4 in 2022, moving to LGA to improve electrical reliability and support DDR5. However, AM4 remains widely used. Many AM4 pins (VDD_CORE, VSS, PCIe, DDR4) are electrically compatible with future CPUs only if voltage regulators support extended ranges (e.g., 1.8V I/O for DDR5 is not possible). X570 chipsets)

| Pin | Signal Name | Group | Notes | |-----|-------------|-------|-------| | A01 | VSS | Ground | | | A02 | VDD_CORE | Core power | | | A03 | VDD_CORE | Core power | | | A04 | VSS | Ground | | | A05 | MEM_DQ_A0 | DDR4 CH A data bit 0 | | | A06 | MEM_DQS_A0_t | DDR4 strobe true | | | A07 | MEM_DQS_A0_c | DDR4 strobe complement | | | A08 | VDD_MEM | Memory power | | | A09 | VSS | Ground | | | A10 | PCIE_RX0_D0 | PCIe lane 0 receive | |

| Feature | CPU (e.g., 5900X) | APU (e.g., 5700G) | |---------|------------------|-------------------| | PCIe lanes usable | 20 (16+4) | 16 (8+4+4?) – actually 20 but with reduced GPU lanes | | Display outputs | Not present | DP, HDMI (eDP) pins | | VDD_GFX pins | NC (no connect) | Active power for GPU | | FCH interface | PCIe x4 | PCIe x4 (same) | | FCLK / UCLK | Unlocked | Same |

The AM4 CPU has pins protruding from the substrate, while the motherboard socket contains spring contacts. This contrasts with AM5 (LGA1718) which switched to LGA. The 35×35 grid would normally yield 1225 positions, but with additional pins around the edges, total reaches 1331. Pins are designated as A01–A35, B01–B35, …, AJ01–AJ35 (lettered rows, numbered columns). Not all positions are populated; keying voids prevent incorrect CPU insertion.