I'm not positive what the question is but since nobody else replied yet I'll take a shot. I have made various signal level convertes in the past. If you want true 5V high you need to use a CMOS chip. If coming from TTL or 3.3V CMOS you need TTL input threshold device such as 74HCT. That give about rail at 20uA or .7 drop at 4mA. 74ACT is .8V drop at 24mA so will give better high level under load. On Thu, Feb 16, 2023 at 10:04:20AM -0500, Neil Cherry via vcf-midatlantic wrote:
This is not a RS232 USB dongle which has it's own issues with interfacing to older equipment (but same problem, no enough current to push or pull the signal).
I have a 3v3/5v0 USB TTL dongle. It works with some equipment but it couldn't pull the signal to 5v0 interfacing to my HD6303 (Hitachi's 6803). I fixed this by using 2 gates on a 74LS04 with the USB dongles TX.
Not sure how to solve this. Has anyone built such a set of line drivers?
I'll be using a similar setup with a few other boards (EPROM burner, PT69-5, Microbox II, etc.). But those might be worse as I'll be using a ESP WiFi chip (3v3) as a terminal server.
-- Linux Home Automation Neil Cherry kd2zrq@linuxha.com http://www.linuxha.com/ Main site http://linuxha.blogspot.com/ My HA Blog Author of: Linux Smart Homes For Dummies KD2ZRQ