# Configurable HD44780 command delay (PR #7356) - feedback/review wanted **URL:** \ **Category:** Features\ **Created:** [September 22, 2026, 2:19pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291 "2026-09-22T14:19:43Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![SirDeath81](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SirDeath81](https://klipper.discourse.group/u/SirDeath81)\ **Post date:** [September 22, 2026, 2:19pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/1 "2026-09-22T14:19:43Z")
I’ve submitted a small PR making the HD44780 LCD command delay configurable: [hd44780: Make command delay configurable by SirDeath81 · Pull Request #7356 · Klipper3d/klipper · GitHub](https://github.com/Klipper3d/klipper/pull/7356) Background: the hd44780.py driver has a hardcoded 40us minimum delay between commands sent to the display. That’s fine for genuine HD44780 chips (Hitachi datasheet minimum is ~37us), but some cheap “clone” displays (in my case an ACM2004 4x20 character LCD) need more margin to display reliably. Previously the only fix was hand-patching the hardcoded constant in hd44780.py. The PR adds an optional `hd44780_delay` config option to the [display] section, defaulting to the existing 40us so nothing changes for users who don’t set it. Tested on a live multi-printer setup: two printers with conforming displays stayed on the 40us default, a third with the non-conforming clone display now uses hd44780\_delay: 0.000050 and displays reliably - no more manual source patching needed. It’s a tiny, backward-compatible change (2 files, +8/-1 lines), but since HD44780 displays are common in the RepRapDiscount/budget printer space, I think it’s worth a look. Happy to answer questions or adjust based on feedback. ---
**Author:** ![hcet14](https://avatars.discourse-cdn.com/v4/letter/h/ecd19e/32.png) [@hcet14](https://klipper.discourse.group/u/hcet14)\ **Post date:** [September 22, 2026, 9:06pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/2 "2026-09-22T21:06:28Z")
Your first post but already a PR, funny. Welcome. I really hope there is a reviewer. I think you code is the right approach since the default 40us value is still set. [HD44780 LCD displays garbage (protocol timing issue, PR 5318)](https://klipper.discourse.group/t/hd44780-lcd-displays-garbage-protocol-timing-issue-pr-5318/25794) you might ask @Dampfwalze for reviewing. It’s a known issue with some HD44780 clones. [hd44780: Make delays configurable by user. by seho85 · Pull Request #5318 · Klipper3d/klipper · GitHub](https://github.com/Klipper3d/klipper/pull/5318) you might have a look at the comments from KevinOConnor. He is the only one who really understands Klipper. Maybe a warning should/could be added in your doc changes and in your hd44780.py changes. Not every Klipper user is able to understand python code, so what should they change? ---
**Author:** ![SirDeath81](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SirDeath81](https://klipper.discourse.group/u/SirDeath81)\ **Post date:** [September 23, 2026, 1:05pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/3 "2026-09-23T13:05:49Z")
Thanks for the pointer, @hcet14 — really appreciated. I hadn’t seen PR #5318, and I want to make sure this attempt actually addresses KevinOConnor’s concerns from back then rather than repeating them. I’ve just pushed an update: 1. Configurability risk: hd44780\_delay is now capped at 0.001s (1ms) via maxval, so it’s no longer possible to set a value large enough to meaningfully stall the mcu task queue - the config parser will reject anything above that with a clear error instead of silently accepting a dangerous value. 2. Guidance for non-technical users: the Config\_Reference.md entry now explains what the symptom looks like (garbled/randomly changing characters), suggests raising the value in small steps from the 40us default, and says to use the lowest value that works - no Python knowledge required. Unlike PR #5318 (which added two separate delay knobs - hd44780\_init\_delay and hd44780\_pin\_delay), this PR only exposes the single existing HD44780\_DELAY constant that was already there and already used for every command - it’s not introducing new timing concepts, just making the existing one adjustable within a bounded, documented range. Root-causing exactly which clone chips/wiring combinations need more margin is a fair ask, but in the meantime this gives affected users (my own case: an ACM2004 clone at 50us) a safe, bounded way to fix it without patching source. @Dampfwalze - if you have time to take a look, it would be very welcome. P.S.: And thanks for the welcome. Until now I was just a reader because I found everything I needed 🙂 ---
**Author:** ![Dampfwalze](https://avatars.discourse-cdn.com/v4/letter/d/ecccb3/32.png) [@Dampfwalze](https://klipper.discourse.group/u/Dampfwalze)\ **Post date:** [September 26, 2026, 11:15pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/4 "2026-09-26T23:15:58Z")
My solution since was to bind mount the source file in question into the Klipper docker container, to replace it with the one from the old PR (since I prefer running with ~~Docker~~ Podman). But this will break eventually, so I am very happy to see movement. This new PR is more clean, so I prefer it. Functionally they are identical. The additional initialization delay that the old PR introduced, I see that as a separate issue. LGTM. I am not a maintainer though, nor did I ever contribute to Klipper. I am just a programmer who happens to have a DIY 3D printer. So these are just my two cents. ---
**Author:** ![SirDeath81](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SirDeath81](https://klipper.discourse.group/u/SirDeath81)\ **Post date:** [September 27, 2026, 11:25am UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/5 "2026-09-27T11:25:03Z")
Thanks for testing/confirming, @Dampfwalze — good to know it’s not just my own setup. Agreed the old PR’s extra init delay is a separate concern; keeping this one scoped to just the existing HD44780\_DELAY constant was intentional. ---
**Author:** ![SirDeath81](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SirDeath81](https://klipper.discourse.group/u/SirDeath81)\ **Post date:** [September 28, 2026, 5:12am UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/6 "2026-09-28T05:12:34Z")
Update: Kevin has reviewed PR #7356. His concern is that a free-form delay value is a “foot gun” (too high a value can cause sporadic, hard-to-debug timeouts), and he suggested a simple on/off option that applies a fixed, known-safe extra delay for clone chips instead. I’m happy to rework the PR that way, but I need to pick a fixed value that covers more than just my own display. So a request to everyone with an HD44780-type display that shows garbled or random characters: - Which display/module do you have (name or marking, if known)? - Which delay made it work reliably for you? My ACM2004 works at 50us (default is 40us). @Dampfwalze - you’re the most important data point here, since you’ve been running a different clone display with the patched file from PR #5318. Which delay value(s) do you need for yours to work? I’ll wait for your answer before updating the PR. Thanks! ---
**Author:** ![hcet14](https://avatars.discourse-cdn.com/v4/letter/h/ecd19e/32.png) [@hcet14](https://klipper.discourse.group/u/hcet14)\ **Post date:** [September 30, 2026, 7:27pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/7 "2026-09-30T19:27:11Z")
Congrats, your first PR and just merged. ---
**Author:** ![SirDeath81](https://avatars.discourse-cdn.com/v4/letter/s/c5a1d2/32.png) [@SirDeath81](https://klipper.discourse.group/u/SirDeath81)\ **Post date:** [October 3, 2026, 6:36pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/8 "2026-10-03T18:36:31Z")
Yes 🙂 Thanks a lot for pointing the way! ---
**Author:** ![hcet14](https://avatars.discourse-cdn.com/v4/letter/h/ecd19e/32.png) [@hcet14](https://klipper.discourse.group/u/hcet14)\ **Post date:** [October 6, 2026, 5:37pm UTC](https://klipper.discourse.group/t/configurable-hd44780-command-delay-pr-7356-feedback-review-wanted/26291/9 "2026-10-06T17:37:35Z")
Hopefully your PR ends problems with HD44780 clones regarding Klipper. Thanks to all involved.