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circuit
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Posted: 06:01am 29 Jul 2023

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To date, I have connected conventional PS2 key boards to MicroMite Extremes but now wish to wire up for the USB Keyboard connection. I am, however, a little confused by the configuration. The datasheet for the PIC32MZ2048 shows:

Pin No.
73 VBUS
74 VUSB3V3
75 VSS
76 D-
77 D+
78 RPF3/USBID/RF3

It is the power voltage issue that confounds me. PIN73 is 5v tolerant but the rest are not. USB is usually 5v, but perhaps sometimes USB keyboards can run on 3v3. Do I simply provide 5v at PIN73 and connect this to the USB connector to the keyboard? Is level conversion needed for the other pins?

I don't understand the relationship between pins 73 and 74 ...help please?

phil99

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Posted: 08:33am 29 Jul 2023

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If it is like the PIC32MX270 MM2 which uses a USB console, the VBUS pin monitors the USB 5V supply and the VUSB3V3 pin monitors the 3.3V supply to the chip.

circuit
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Posted: 10:29am 29 Jul 2023

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phil99 said If it is like the PIC32MX270 MM2 which uses a USB console, the VBUS pin monitors the USB 5V supply and the VUSB3V3 pin monitors the 3.3V supply to the chip.

I am unaware of a MicroMite based upon the PIC32MX270 which enables a USB keyboard. Please elaborate?

All I wish to know is which processor pins connect to which USB pins on the PIC32MZ2048 (MicroMite Extreme) chip and where I should feed in 5V for the USB to keyboard connection.

Mixtel90

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Posted: 10:42am 29 Jul 2023

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For the PIC32MZ in host mode (it's actually always running in OTG mode) the VBUS pin must be connected to 5V.
https://microchipdeveloper.com/faq:3233

VUSB3V3 is the 3V3 supply to the on-chip USB module.

Here is an example schematic.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

circuit
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Posted: 10:56am 29 Jul 2023

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Mixtel90 said For the PIC32MZ in host mode (it's actually always running in OTG mode) the VBUS pin must be connected to 5V.
https://microchipdeveloper.com/faq:3233

VUSB3V3 is the 3V3 supply to the on-chip USB module.
/QUOTE]

Thank you for that; immensely helpful, that is the connection that I suspected was right, but it suggests that the data pins would be operating at 5v - perhaps I do not understand USB properly.
Where is my thinking incorrect?

Mixtel90

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Posted: 11:35am 29 Jul 2023

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D+ and D- only have a nominal voltage - at about 3V. The voltage has nothing to do with VBUS. The transmitter treats them as a differential pair. They normally have pullups to about 3V6.
https://www.beyondlogic.org/usbnutshell/usb2.shtml
Edited 2023-07-29 21:37 by Mixtel90

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

phil99

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Posted: 12:14pm 29 Jul 2023

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MX270 MM2 thread It doesn't use USB for a keyboard, it's for the link to the terminal.
However it appears to use the same connections as the MZ.

circuit
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Posted: 01:22pm 29 Jul 2023

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Mixtel90 said D+ and D- only have a nominal voltage - at about 3V. The voltage has nothing to do with VBUS. The transmitter treats them as a differential pair. They normally have pullups to about 3V6.
https://www.beyondlogic.org/usbnutshell/usb2.shtml

Mick, thank you. After I puzzled over this immediately after my last posting, the concept of "differential pair" clicked - and I grew donkey ears immediately for not remembering how all this works.

All now clear in my mind and USB keyboard connected up.

circuit
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Posted: 01:26pm 29 Jul 2023

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phil99 said MX270 MM2 thread It doesn't use USB for a keyboard, it's for the link to the terminal.
However it appears to use the same connections as the MZ.

Well, that is a revelation! This was a thread that I had no knowledge of. This makes me wonder what other developments are on this forum that have withered into the distance of time. A fascinating and most interesting innovation. Thank you for the link.

Mixtel90

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Posted: 01:47pm 29 Jul 2023

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I didn't know about that either (or I'd completely forgotten about it - wouldn't be surprised!), you aren't alone. :)
Edited 2023-07-29 23:47 by Mixtel90

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

circuit
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Posted: 07:32pm 03 Aug 2023

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Well, I have the USB keyboard connected and operating, BUT
with a simple programme running at start-up (OPTION AUTORUN ON), the CTRL-C break does not work and neither does any other key.
OPTION AUTORUN OFF and reboot the system and the keyboard works - all keys okay.
RUN the programme, CTRL-C functions okay and breaks the programme. RUN the same programme again and the keyboard is okay. Run it a third time and the keyboard is dead again.
Restart with OPTION AUTORUN ON and the keyboard functions not.

All connections are soldered and seem okay, as do the voltage levels. Problem is repeatable. When the keyboard is operating it hot-plugs just fine.

Programme could not be simpler;

DO
LOAD "IMAGE01.BMP"
PAUSE 5000
LOAD "IMAGE02.BMP"
;code repeated to image 10
PAUSE 5000
LOOP

Display is SSD1963

Any ideas welcome...

phil99

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Posted: 11:05pm 03 Aug 2023

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Does the MZ have a Library? If so instead of OPTION AUTORUN ON put this sub in it and see what happens. If there is no library adding it to the program may work.

Sub MM.Startup
Run
End Sub

circuit
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Posted: 07:20pm 04 Aug 2023

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The problem became more erratic with different scenarios leading me to think that this is not a software/firmware issue. After various permutations I tracked it down to a marginal 5v supply brought about by the USB cable feeding power to the unit. When I intercepted the 5V connection to the keyboard USB connection I found that the voltage dropped below 4.5v. When it was 4.6v all seemed okay. 4.4v and I had keyboard failure.

I concluded that when the programme read from the SD card and the screen was refreshing the USB power lead was not providing sufficient current and therefore the voltage was dropping below that at which the keyboard would operate.

Incidentally, I started checking the 5V output on a number of my USB leads and some of the raw voltage drops from a 5V supply were astonishing! I will have to sort the wheat from the chaff or buy some better USB leads!

Thanks, Phil99, for the suggestion anyhow - and yes, the MZ does have library; one of the reasons I really like the chip.

Mixtel90

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Posted: 07:38pm 04 Aug 2023

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The CMM2 is notorious for drawing enough current to upset typical USB A-B leads. Many of these leads are not designed with any current capability as the 5V supply will normally be present on the remote device (often a printer) as well as the PC. It looks like you've come up against the same problem.

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

circuit
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Posts: 245

Posted: 10:47am 05 Aug 2023

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Mixtel90 said The CMM2 is notorious for drawing enough current to upset typical USB A-B leads. Many of these leads are not designed with any current capability as the 5V supply will normally be present on the remote device (often a printer) as well as the PC. It looks like you've come up against the same problem.

Mick, thank you for that additional information - a problem that I had not come across before with less demanding chips/displays.

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