From eef535f9ef76c1bb6498dd2f63a9535f9088ce3f Mon Sep 17 00:00:00 2001 From: Me Here Date: Mon, 1 Jun 2026 13:04:42 -0500 Subject: [PATCH] DESIGN: route LCD TE pin on production face for tear-free updates MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit ST7796S datasheet §10.8: panel rescans GRAM at 60Hz; tear-free writes require feeding the TE output back to the MCU and writing during vblank. EP-0172 prototype wires no TE, so large updates tear (small writes hide it — why MP/CP look clean). Add TE (e.g. GP4) + optional MISO to the face interconnect for the production board. Co-Authored-By: Claude Opus 4.8 (1M context) --- hardware/DESIGN.md | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/hardware/DESIGN.md b/hardware/DESIGN.md index 35a3793..c4dcdc3 100644 --- a/hardware/DESIGN.md +++ b/hardware/DESIGN.md @@ -172,6 +172,16 @@ Grounds interleaved around SPI. A Pico/Pico 2 test adapter maps these to the lis on-core — they are not on the ribbon. A Pico test brain drives the digital/face I/O above but **cannot** drive the analog chain (DAC/op-amps are core-only).* +> **Display TE line — route it on the production face.** The table above mirrors the EP-0172 +> prototype, which wires only SCK/MOSI/CS/DC/RST and **no TE (tearing-effect) output**. Per the +> ST7796S datasheet §10.8, the panel rescans its frame memory to the glass at 60 Hz and the *only* +> sanctioned way to avoid tearing is to feed the **TE output back to the MCU** and write during +> vblank (`tvdh`). Without it, large updates tear and only small sub-region writes hide it (this is +> why MicroPython/CircuitPython, which draw glyph-by-glyph, look clean and the Rust full-frame blits +> don't). **Add the LCD `TE` pin to a spare GPIO (e.g. GP4)** on the face interconnect — and +> optionally LCD `MISO`/`SDO` for `GSCAN`(45h)/status reads. Then firmware can do +> `TEON`(35h)+vblank-synced writes and be fully tear-free even on full repaints. + ### 7.2 Analog audio interconnect — 2×5 (10-pin), twisted/shielded, away from digital | Pin | Signal | | Pin | Signal | |----|--------|--|----|--------|