diff --git a/hdl/logic-analyzer/README.md b/hdl/logic-analyzer/README.md
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+# Logic-analyzer capture memory
+
+`rtl/la_capture_buffer.v` is a portable Verilog-2001 true dual-port capture
+buffer.  It deliberately contains no Altera/Intel primitive, board pin, UART,
+or trigger logic.  Quartus infers Cyclone IV M9K memory from the registered
+read and synchronous write ports.
+
+Parameters:
+
+| Parameter | Meaning | Default |
+|---|---|---:|
+| `SAMPLE_WIDTH` | Number of simultaneously captured digital inputs | 16 |
+| `ADDR_WIDTH` | Buffer depth as `2**ADDR_WIDTH` | 12 (4096 samples) |
+
+The write and read clocks may be different.  The caller owns clock-domain
+crossing for addresses/status and must keep a read address stable until the
+registered `rd_data` is valid on the following `rd_clk` edge.
+
+Example Quartus source assignment:
+
+```tcl
+set_global_assignment -name VERILOG_FILE path/to/templates/hdl/logic-analyzer/rtl/la_capture_buffer.v
+```
diff --git a/hdl/logic-analyzer/rtl/la_capture_buffer.v b/hdl/logic-analyzer/rtl/la_capture_buffer.v
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+// Portable dual-clock capture RAM for FPGA logic analyzers.
+// The module intentionally contains no vendor primitives: Quartus infers M9K
+// blocks on Cyclone IV, while other tools may infer their native block RAM.
+module la_capture_buffer #(
+    parameter SAMPLE_WIDTH = 16,
+    parameter ADDR_WIDTH   = 12
+) (
+    input  wire                    wr_clk,
+    input  wire                    wr_en,
+    input  wire [ADDR_WIDTH-1:0]   wr_addr,
+    input  wire [SAMPLE_WIDTH-1:0] wr_data,
+
+    input  wire                    rd_clk,
+    input  wire [ADDR_WIDTH-1:0]   rd_addr,
+    output reg  [SAMPLE_WIDTH-1:0] rd_data
+);
+    localparam DEPTH = (1 << ADDR_WIDTH);
+
+    reg [SAMPLE_WIDTH-1:0] memory [0:DEPTH-1];
+
+    always @(posedge wr_clk) begin
+        if (wr_en)
+            memory[wr_addr] <= wr_data;
+    end
+
+    // Registered read is supported directly by Cyclone IV M9K blocks.
+    always @(posedge rd_clk)
+        rd_data <= memory[rd_addr];
+endmodule