On 2/16/23 16:38, David Gesswein via vcf-midatlantic wrote:
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.
Basically I'm looking to build some kind of standard board to allow me to use the USB TTL dongle (CH341) to hook up to my vintage computers without having to go '3v3/5v0 TTL' to RS232 back down to 5v0 TTL. I tried the Adafruit converter but it didn't have the current to drive the serial into the HD6303. On another mail list someone has suggested looking at CD74HC4049 and CD74HC405. I forgot about those chips. Some of the more interesting chips are 16 bits wide. A bit (14) more than I need. The good news is that the 74LS04 is working nicely. I've got the 8K RAM added and I'm writing 6801 asm code. These LEDs are driven in a strange way. The 2 - 7 Segmented LEDs and the 7 individual LEDs are driven by the same 8 bits. -- 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