diff --git a/docs/tec1g-emulation-review.md b/docs/tec1g-emulation-review.md
index 65d7a0c..c986f13 100644
--- a/docs/tec1g-emulation-review.md
+++ b/docs/tec1g-emulation-review.md
@@ -405,7 +405,7 @@ Disco LEDs (Fullisik under mechanical keys) — **N/A**
 | Matrix keyboard           | Med  | **Complete**        | 100% |
 | CONFIG DIP switch         | Low  | **Complete**        | 100% |
 | RTC (DS1302)              | Low  | **Complete**        | 100% |
-| SD card SPI               | Low  | **Missing**         | 0%   |
+| SD card SPI               | Low  | **Complete**        | 95%  |
 | Cartridge                 | Low  | **Partial**         | 40%  |
 | Joystick                  | Low  | **Missing**         | 0%   |
 | Status LED bar            | Low  | **Missing**         | 0%   |
@@ -767,7 +767,6 @@ External add-on emulation. Fully independent of other stages.
 - [x] Add `sdEnabled: boolean` and optional `sdImagePath: string` config options
 - [x] Instantiate `SdSpi` in runtime when enabled
 - [x] Route port 0xFD writes to `sdSpi.write(value)`, reads to `sdSpi.read()`
-- [ ] If `sdImagePath` provided, load file as virtual disk image for block reads
 - [x] If `sdImagePath` provided, load file as virtual disk image for block reads
 - [x] Add SD presence indicator to SYS_INPUT (not applicable — no dedicated bit in schematic)
 - [x] Unit tests: end-to-end port 0xFD initialization sequence
diff --git a/src/platforms/tec1g/README.md b/src/platforms/tec1g/README.md
index 138be4c..4f326d6 100644
--- a/src/platforms/tec1g/README.md
+++ b/src/platforms/tec1g/README.md
@@ -71,8 +71,8 @@ The TEC-1G panel can switch speed modes; the serial timing assumes FAST mode.
   - Bit 4: FF-D4 (reserved — not yet decoded).
   - Bit 5: CAPS (caps lock — not yet decoded).
   - Bits 6-7: FF-D5/FF-D6 (reserved — not yet decoded).
-- `OUT 0xFC`: RTC DS1302 (stub — not yet emulated, reads return 0xFF).
-- `OUT 0xFD`: SD card SPI (stub — not yet emulated, reads return 0xFF).
+- `OUT 0xFC`: RTC DS1302 (bit-banged emulation).
+- `OUT 0xFD`: SD card SPI (bit-banged emulation, SPI mode).
 
 ## Serial (bitbang)
 - TX uses bit 6 on `OUT 0x01`; RX uses bit 7 on `IN 0x00` (mirrored on `IN 0x03`).
diff --git a/src/platforms/tec1g/sd-spi.ts b/src/platforms/tec1g/sd-spi.ts
index 883ba05..f5cb111 100644
--- a/src/platforms/tec1g/sd-spi.ts
+++ b/src/platforms/tec1g/sd-spi.ts
@@ -11,6 +11,7 @@ type SdCommand = {
 export type SdSpiOptions = {
   csMask?: number;
   csActiveLow?: boolean;
+  highCapacity?: boolean;
   image?: Uint8Array;
 };
 
@@ -24,6 +25,7 @@ const DEFAULT_CS_MASK = 0x04;
 export class SdSpi {
   private csMask: number;
   private csActiveLow: boolean;
+  private highCapacity: boolean;
   private csActive = false;
   private clk = false;
   private inShift = 0;
@@ -47,6 +49,7 @@ export class SdSpi {
   public constructor(options: SdSpiOptions = {}) {
     this.csMask = options.csMask ?? DEFAULT_CS_MASK;
     this.csActiveLow = options.csActiveLow !== false;
+    this.highCapacity = options.highCapacity !== false;
     this.image = options.image ?? null;
   }
 
@@ -229,7 +232,8 @@ export class SdSpi {
         break;
       }
       case 58: {
-        this.pendingResponse = [this.ready ? 0x00 : 0x01, 0x40, 0x00, 0x00, 0x00];
+        const ocr = this.highCapacity ? 0x40 : 0x00;
+        this.pendingResponse = [this.ready ? 0x00 : 0x01, ocr, 0x00, 0x00, 0x00];
         this.delayBytes = 1;
         break;
       }
@@ -253,7 +257,8 @@ export class SdSpi {
   }
 
   private readBlock(arg: number): number[] {
-    const start = arg >>> 0;
+    // SDHC uses block (LBA) addressing; SDSC uses byte addressing.
+    const start = this.highCapacity ? ((arg >>> 0) << 9) >>> 0 : (arg >>> 0);
     const payload = new Array<number>(512).fill(0x00);
     if (!this.image || this.image.length === 0) {
       return payload;
diff --git a/tests/platforms/tec1g/sd-spi.test.ts b/tests/platforms/tec1g/sd-spi.test.ts
index aeeb4fe..087edcf 100644
--- a/tests/platforms/tec1g/sd-spi.test.ts
+++ b/tests/platforms/tec1g/sd-spi.test.ts
@@ -123,4 +123,25 @@ describe('SdSpi', () => {
     expect(readByte(spi)).toBe(0x00);
     expect(readByte(spi)).toBe(0x5a);
   });
+
+  it('treats CMD17 argument as block address for high capacity cards', () => {
+    const image = new Uint8Array(2048);
+    image[0x0202] = 0xa5;
+    const spi = new SdSpi({ csMask: CS_BIT, image, highCapacity: true });
+    writeSpi(spi, 0x00);
+    sendCommand(spi, [0x77, 0x00, 0x00, 0x00, 0x00, 0x65]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x69, 0x40, 0x00, 0x00, 0x00, 0x77]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x77, 0x00, 0x00, 0x00, 0x00, 0x65]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x69, 0x40, 0x00, 0x00, 0x00, 0x77]);
+    readResponseByte(spi);
+    sendCommand(spi, [0x51, 0x00, 0x00, 0x00, 0x01, 0xff]);
+    expect(readResponseByte(spi)).toBe(0x00);
+    expect(readByte(spi)).toBe(0xfe);
+    expect(readByte(spi)).toBe(0x00);
+    expect(readByte(spi)).toBe(0x00);
+    expect(readByte(spi)).toBe(0xa5);
+  });
 });