On Thu, Dec 2, 2021 at 10:56 AM, Harvey White wrote:
Couple things on USB that might help.
You can easily buy a TTL to USB converter.? Takes TTL level (as from
uart/usart) signals, either 3.3 or 5.0 volts, and translates them to a
USB signal.? That USB signal, when plugged into a PC, enumerates as a
serial port.? You set the baudrate at the terminal to match the TTL
baudrate.
In a number of microprocessor boards (my experience is with the ST-MICRO
boards), the USB chip on the board used for programming also has a
virtual terminal function (at the same time as debugging).? The USB chip
is hardwired to a USART output on the processor.? If you don't use those
pins for something else, and don't disconnect them, you can initialize
that particular USART on the processor and use it to communicate through
the debugging cable.? Your debugging system runs an instance of a
terminal program.
In addition, if you enable the fprint functions in your system and
direct them to the USB usart channel, you can get ongoing outputs from
the processor to the computer for monitoring a process.? You could also
use the console in and out functions, but those may need to be
redirected in your program.
Really easier than you might think.
As to emulating a true HID device, I haven't tried that, haven't needed
to, but I suspect with the right drivers, emulating an HID device
(mouse, etc) might be easy enough.
Harvey
On 12/2/2021 12:07 PM, Chris Wilkson via groups.io wrote:
This is fantastic work, Holger!
I have a disembodied P7001 that I keep meaning to add to a 7704 so I can
play with it. Or, finally accept that I will never get to it and pass the
p7001 to a new owner.
Your project tilts my internal debate toward "keep it". :)
Quick question on Teensy: Can it be configured as a USB HID host?
I have many homebrew projects that would benefit from a USB keyboard-to-TTL
converter but I'm honestly intimidated by USB complexity so I haven't done
much research on USB hosts.
Hi Harvey,
My need is actually in the other direction. There is no PC involved anywhere.
There are a million ways to connect a random electronics project to a PC through USB, typically using an FTDI IC with a virtual com port in Windows. Which is the way you described. Or using a development board from an MCU manufacturer or something in the Arduino ecosystem. But cursory searches turn up little info on preexisting solutions for connecting commercial USB devices (keyboard, mouse, usb stick, whatever) to a random electronics project.
Here's an example of what I want to do. I have a working USB keyboard (standard COTS device) that I want to interface to a vintage CPU. Say a 6502 for example. Or even to a discrete TTL design. So I need a USB *host* that can talk to the keyboard and spit out raw data on the other side in serial or preferably parallel format. I went down the PS2 -> TTL route years and years ago. It was fairly trivial. But USB host implementation is a whole different animal.
Best,
Chris
