[PIC] Using USB with the 18F4520!

Discussion:

Clint Jay

2017-11-14 12:47:26 UTC

There may be, I've usually just rolled my own routines to service the
EUSART though I haven't used the '4520 specifically.

I don't think there are huge differences between most EUSART enabled mid
range devices so there should be plenty of example code to examine and
modify for your needs.

You'll need a level translator if you're going PIC to PC directly.

Clint,
Yes, I am using a FTDI to RS232 converter to hook the PC to the
PIC. I just found out that all that I need to do is treat the connection
to the PIC as a Serial connection. Is there a MC Serial Library
available? I'm the one that was confused.
Thanks,
rich!

I'm a little confused but the way I read your message would suggest that
you're going to connect your PIC to the PC with an FTDI USB to serial
device?
Or have I misunderstood and you're hoping to connect the PIC to the FTDI
with USB?
HELLO ALL,
. . . . I could really use some help with using USB on the PIC 18F4520.
I am going to use a FTDI USB to RS232 converter to talk to the PIC
18F4520 Through the RX and TX Pins. I want to send Configuration Code to
a 24C512 serial EPROM. When I add additional devices I want to be able
to update the EPROM. I also want to be able to use a Win 8.1 64bit Pro
PC to control the Programmer. I also do a lot of searching and research
on materials that I acquire from the MicroChip website. I have been
reading the MC USB Device Firmware Framework User's Guide.
. . . . I have the latest version of MpLab, and the latest versions of
the X8, X18, and X32 Compilers installed. I also see that I need to
install the latest versions of C30 C and C18 C Compilers and setup the
proper Paths for these files. I don't mind doing the footwork. I am
Disabled and retired. This gives me a lot of free time.
Thanks,
Richard R. Pope
1230 19th Street #5
Reedsburg, WI 53959, USA
1-608-768-7448
---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus
--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

Richard Pope

2017-11-14 12:56:17 UTC

Permalink

Clint,
I'll do that this evening after I get up. I appreciate the insight
and help! I will probably have to use a MAX232 to do the level
translation. I appreciate you reminding me of that.
Thanks,
rich!

Post by Clint Jay
There may be, I've usually just rolled my own routines to service the
EUSART though I haven't used the '4520 specifically.
I don't think there are huge differences between most EUSART enabled mid
range devices so there should be plenty of example code to examine and
modify for your needs.
You'll need a level translator if you're going PIC to PC directly.

--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

Anthony Nixon

2017-11-14 13:54:26 UTC

Permalink

You wont need a level translator with the FTDI chip. It will directly
interface to the PIC, and the FTDI directly interfaces to the USB port
with the right support components which are just a handful of
passives.

The trick is whether or not the FTDI will be powered by the USB port
or by the PIC circuit.

cheers

Tony

--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

Byron Jeff

2017-11-14 14:54:47 UTC

Permalink

Tony,

There are actually two types of FTDI serial ports. There is the RS232 one
with a DB9 connector on the end. Typically that port will signal between
+/- 7 volts or so. Then there are the small FTDI TTL serial adapters.
Depending on configuration they will swing either between 0 and 5 volts or
0 and 3.3 volts.

In today's serial PC world rarely does an actual MAX232 need to be used for
level translation. Even with actual RS232 ports, virtually all of them
signal properly with a 0/5V TTL signal. Note that the sign is inverted such
that a logical 1 is represented by 0V and a zero by 5V.

For years I've used a simple voltage clamp to limit the swings. The basic
circuit is here: Loading Image...

D1 conducts when Vin
is above VMax and D2 conducts then Vin is below Vmin. R limits the current.
I typically put a second resistor after the clamp. I find that 1K for both
works well with PIC inputs.

A couple of variations are helpful. If D1 and D2 are Schotty diodes then
the voltage overshoot is typically only 0.3V or so. Also if D2 is a Zener
then D1 is unnecessary because the Zener action will limit the high voltage
while normal conduction clamps the low voltage.

With the signal inverted there are a few things you can do to manage it.
I've been using PIC24FV parts for several years. The hardware EUARTS on
them can be inverted in software. It is also possible to bit bang a digital
input/output for serial. Otherwise a NPN transistor whose base is connected
to Vout, emitter grounded, and a pullup collector will invert the signal in
hardware.

Another thought that may be traitorous on this board: ever considered an
Arduino? Complete boards with the USB serial adapter on board clock in at
about $5 USD. Boards like a Nano will plug right into a breadboard. Plug in
a USB cable, load the Arduino IDE and you're going literally in about 5
minutes. Tons of libraries already built into the platform.

As I've progressed in the hobby, I find that sometimes it's just more
trouble than it's worth to try to roll everything from scratch. Back in the
PIC 16C54 days, the price and functionality was a compelling reason to
switch as compared to the alternatives. But in 2017 with high level boards
such as a Raspberry PI Zero W that runs Linux and having a complete wireles setup
for less than $10 USD and Arduino clones literally running 5 for $20, it
becomes more difficult to justify wiring up a board from scratch and
programming in assembly anymore. Those who have never done it may need the
experience. But those of us who have a closetfull of t-shirts with
'Assembly coder' emblazoned upon them? Not so much. I find now that I spend
more time and energy trying to match the hardware/firmware to the
application. It literally may be more adventageous to throw a RasPi ZeroW
into a problem to make a wireless remote light switch than any alternative for
example.

BAJ

Post by Anthony Nixon
You wont need a level translator with the FTDI chip. It will directly
interface to the PIC, and the FTDI directly interfaces to the USB port
with the right support components which are just a handful of
passives.
The trick is whether or not the FTDI will be powered by the USB port
or by the PIC circuit.
cheers
Tony

--
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist

Clint Jay

2017-11-14 15:04:26 UTC

Permalink

Jeff, you raise good points but I would prefer to be safe than sorry,
designing/building and coding for the MAX232 or other serial driver will
ensure compatibility (as far as RS-232 is able to be compatible) with the
widest range of PCs and prevent anything 'unpleasant' happening if the
device is plugged into an unknown machine.

As heretical as it would seem I'd have to admit you may have a point about
Arduino, it's a known hardware platform that is proven to work.

Similarly, I've been exploring options with STM32 Blue Pill boards recently
but I still like and write code for PIC devices, as and when I need extra
horsepower I may well leave the PIC Path and move to ARM, they're *so*
cheap and have an abundance of facilities.

Post by Byron Jeff
Tony,
There are actually two types of FTDI serial ports. There is the RS232 one
with a DB9 connector on the end. Typically that port will signal between
+/- 7 volts or so. Then there are the small FTDI TTL serial adapters.
Depending on configuration they will swing either between 0 and 5 volts or
0 and 3.3 volts.
In today's serial PC world rarely does an actual MAX232 need to be used for
level translation. Even with actual RS232 ports, virtually all of them
signal properly with a 0/5V TTL signal. Note that the sign is inverted such
that a logical 1 is represented by 0V and a zero by 5V.
For years I've used a simple voltage clamp to limit the swings. The basic
circuit is here: https://i.stack.imgur.com/jyZvD.gif D1 conducts when Vin
is above VMax and D2 conducts then Vin is below Vmin. R limits the current.
I typically put a second resistor after the clamp. I find that 1K for both
works well with PIC inputs.
A couple of variations are helpful. If D1 and D2 are Schotty diodes then
the voltage overshoot is typically only 0.3V or so. Also if D2 is a Zener
then D1 is unnecessary because the Zener action will limit the high voltage
while normal conduction clamps the low voltage.
With the signal inverted there are a few things you can do to manage it.
I've been using PIC24FV parts for several years. The hardware EUARTS on
them can be inverted in software. It is also possible to bit bang a digital
input/output for serial. Otherwise a NPN transistor whose base is connected
to Vout, emitter grounded, and a pullup collector will invert the signal in
hardware.
Another thought that may be traitorous on this board: ever considered an
Arduino? Complete boards with the USB serial adapter on board clock in at
about $5 USD. Boards like a Nano will plug right into a breadboard. Plug in
a USB cable, load the Arduino IDE and you're going literally in about 5
minutes. Tons of libraries already built into the platform.
As I've progressed in the hobby, I find that sometimes it's just more
trouble than it's worth to try to roll everything from scratch. Back in the
PIC 16C54 days, the price and functionality was a compelling reason to
switch as compared to the alternatives. But in 2017 with high level boards
such as a Raspberry PI Zero W that runs Linux and having a complete wireles setup
for less than $10 USD and Arduino clones literally running 5 for $20, it
becomes more difficult to justify wiring up a board from scratch and
programming in assembly anymore. Those who have never done it may need the
experience. But those of us who have a closetfull of t-shirts with
'Assembly coder' emblazoned upon them? Not so much. I find now that I spend
more time and energy trying to match the hardware/firmware to the
application. It literally may be more adventageous to throw a RasPi ZeroW
into a problem to make a wireless remote light switch than any alternative for
example.
BAJ

enabled mid

Post by Anthony Nixon

Post by Clint Jay
range devices so there should be plenty of example code to examine and
modify for your needs.
You'll need a level translator if you're going PIC to PC directly.

Clint,
Yes, I am using a FTDI to RS232 converter to hook the PC to the
PIC. I just found out that all that I need to do is treat the

connection