Calendink/Client/AgentDoc/epd_reference_driver.md

EPD Reference Driver — GDEY075T7 (UC8179)

Source

Repository: ekosboard/firmware
File: src/components/EPD/driver/epd_GDEY075T7.c

Panel Info

• Controller: UC8179
• Panel: GDEY075T7 (Good Display 7.5" B/W, 800×480)
• Platform: ESP-IDF (native SPI)
• Grayscale: 4-level support present but marked as "NOT TESTED"

Key Implementation Details

BUSY Pin Polarity

• Reference driver: HIGH = Busy, LOW = Idle
• ⚠️ Our board is INVERTED: LOW = Busy, HIGH = Idle
• Wait loop polls gpio_get_level(BUSY) == 0 to detect idle (reference)
• Our code uses == 0 to wait while busy (opposite meaning, same code pattern)

Clear Screen (White)

• Writes 0xFF to both old (0x10) and new (0x13) data layers
• 0xFF = White, 0x00 = Black

Display Image

• Writes 0x00 to old data layer (0x10) — assumes previous state was black
• Writes actual image data to new data layer (0x13)

Sleep Sequence

1. 0x50 with 0xF7 — VCOM and data interval setting before sleep
2. 0x02 — Power Off
3. Wait for BUSY idle
4. 0x07 + 0xA5 — Deep Sleep

Init Sequence (Full Refresh)

1. Hardware reset (RST low 10ms, high 10ms)
2. 0x01 — Power Setting: VGH=20V, VGL=-20V, VDH=15V, VDL=-15V, VDHR=4.2V
3. 0x06 — Booster Soft Start: 0x17, 0x17, 0x28, 0x17
4. 0x04 — Power On + 100ms delay + wait busy
5. 0x00 — Panel Setting: 0x1F (KW B/W mode)
6. 0x61 — Resolution: 800×480
7. 0x15 — DUSPI disabled
8. 0x50 — VCOM: 0x10, 0x07
9. 0x60 — TCON: 0x22
10. 0xE3 — PWS: 0x22

Fast Refresh

• 0xE0 → 0x02 (enable fast mode)
• 0xE5 → 0x5A (fast refresh timing)

Partial Update

• Uses 0x91 (partial in) / 0x92 (partial out) + 0x90 (resolution setting)
• Writes ~data (inverted) to old layer to force transitions
• Sets 0x50 → 0x21 (N2OCP disabled) for partial mode

4-Level Grayscale

• Requires different booster settings: 0x27, 0x27, 0x18, 0x17
• 0xE5 → 0x5F for grayscale timing
• Data encoding: 2 bits per pixel (0xC0=white, 0x00=black, 0x80=gray1, 0x40=gray2)
• Old layer and new layer encode different bit planes, both inverted (~temp3)