Subject:
Re: DIY USB programmer ?
From:
####@####.####
Date:
5 Jan 2005 16:30:02 +0000
Message-Id: <10597.1104942571@www8.gmx.net>
> On Tue, Jan 04, 2005 at 06:39:41PM +0100, Manuel Bessler wrote:
> > Hi all,
> >
> > I'm looking for a simple DIY design for a USB-based PIC programmer.
> > (ok that part is easy)
> > ... BUT ... if at all possible such a burner should not require a PIC
> > itself. (the chicken and egg problem :( )
>
> A problem that's as old as time itself.
Low cost solution: use a simple jtag cable. (parallel port or usb2par cable
required), one hc244 required + 16 resistors + 1 cap.
>
> >
> > I have a PIC based Project (called the PIC HomeCockpit Controller, PHCC.
> > Its for the flightsim people who want to build a cockpit at home).
> >
> > Now, most folks who build PHCC don't have a PIC programmer at home, so
> > they need to buy or build one. Of course, the cheaper the better.
> > But due to the demise of parallel port and serial port, the common types
> > (JDM, Tait, BAJ) can't be used.
> > Most new computers only have USB, but no "legacy ports".
>
> I take issue with that statement. While of course PCs are trending to
> having
> between 6 and 8 USB ports, every one that I have seen in recent memory
> have
> had at least one parallel and one serial port.
>
> >
> > I've been wondering if it is possible to build a programmer based on the
> > FTDI FT232BM or FT245BM chips.
>
> Of course. But now you're back to the same issue. By the time you've put
> together a board with these, you've spent way more than the cost of a
> simple PIC programmer anyway. And the task of soldering surface mount
> parts
> is daunting at best.
>
> Also only the FT245 really makes sense because it presents a parallel
> interface. The FT232 fundamentally gives you nothing more than a USB to
> RS232 cable, which we've already seen gives you a complete interface for
> about $10 USD.
>
Even the ft232 can be used as bit bang modus. As i remember, a eeprom must
be
present in order to enable advanced features.
> >
> > The problem here is the timing. USB can't guarantee the timings as far
> > as I understand.
>
> What timings?
Multibyte timings, if programming multible bytes at the same time using a
paging
algorithm, there exist a timeout between the single bytes. Most programming
sw
using this in order to program the device in minor time.
In bit bang mode, the timing for a ftdi chip is 2ms for a single port write
and
1ms for streamed port writes.
So trasmitting one word equals to 25 ms or 50 ms, if some signaling issues
exists,
like caps, or other induction type interface, that compromites the 80ns rise
time.
The new ftdi232C have a internal ms... engine for i2c/spi/jtag/icsp/...
trasmission.
Using it, full speed programming is possible.
The advantage of the bitbang modus is the possibility to use spare pins on
the ftdi
chip and connect it to the other hw without requiring jumpers.
If the cpu can program itself, then burning a 100-250 bytes bootloader on
it,
and then using the hw rs232 port to download the program. Using the external
timed
programming algorithm (sw programming or low voltage programming), then it's
possible
the device in 3-4 seconds, including the bootloader programming and using
the bitbang
modus without the ms... jtag engine.
The ftdi232C have two serial ports or one serial and on parallel, and it's
possible
to reserve one for the firmware update without need of rerouting the signals
or needs
for dedicated programming pins on the MCU.
>
> >
> > I've skimmed the programming specs for two chips, and it looked like
> > most timings don't have a "max" defined. So, would this be possible ?
>
> Would what be possible? Programming PICs is a static activity. If you had
> debounced switches, you could program a PIC by hand.
>
> >
> > What do you guys think ? Could it be possible to build a simple burner
> > that does not need "intelligence" apart from an USB interface chip.
>
> Yes. But you'll still have issues.
>
> Let's table the FT parts for now and discuss the only sensible solution: a
> USB to serial converter cable. They are cheap, complete, readily
> available,
> and presents a standard interface without having to introduce any
> additional
> drivers AFAICT.
>
> The crux of the problem is that RS232 is a asyncronous interface. So there
> is no clock signal that can easily be extracted from the transmitted
> signal.
> Also I don't think it's possible to make any guarantees from the modem
> signals (DTR, RTS, CTS, RI and the like). This is unfortunate because if
> control and timing of those signals relative to the TX line could be
> guaranteed, then a simple programmer could be built using little more than
> a
The serial port has at minimum two input and two output signals, with
direct sw control (rts/cts/dtr).
This works reliable, ie, and don't are asynchronus betweend the two outputs
and two
inputs.
This works mutch faster then the bit bang modus.
Unfortunatly, this pins can be used by the sw, and so extra hw care must be
taken.
On bitbang modus, one can use the input pins for output the clock and data
line.
This eliminates mostly the needs of adding additionally hw protections, if
the pins
are used for other purposed and are not reserved.
> USB/serial converter cable and a MAX232. The DTR line could then be
> connected
> to the PIC program data line and TX connected to the program clock line.
> To program you'd set DTR to the appropriate bit then send a 0xff to clock
> the data. You could also route back the PIC data line to DSR or CTS to
> read back the data from the PIC. It would be a serial analog of my
> parallel
> port based Trivial PIC programmer.
Using the TX/RX lines on a usb converter is not reliable as oppesed to the
pc.
In most case, the tx/rx and the dsr/cts samples are asynchronous and don't
follow
the rules as to the PC.
You should use the other lines .
This works pretty good.
>
> But as I said there are no guarantees of the relationship of the modem
> control signals to TX. So you can't be sure that you can set/reset the
> modem
> control signals. You also cannot be sure that if you can set/reset the
> modem
> control signal that those changes would be in place before you clock TX.
>
> So the only thing that you can guarantee is the TX signal. Fortunately
> there
> are some guarantees there. Because of the async interface you know that
> you'll get really precise timing at any particular bit rate. So you'll
> have
> exact timings relative to the falling edge of the start bit.
>
> So the simplest TX only programmer will require an external one shot to
> clock in the data bit at some time relative to the falling edge of the
> start
> bit.
>
> This is when you trot in the venerable 555 timer. The problem with it is
> that it needs to be non-retriggerable. A 5 minute Google search came up
> with the interesting idea of using an NPN transistor as the gate. Let me
> see if I can describe it:
>
> 1. Wire up the 555 in traditional one shot mode. There are a trillion
> examples of this so I won't describe any further.
>
> 2. Add a NPN transistor to the trigger input of the 555. Wire the
> collector
> to the trigger input (with a pullup resistor), the emitter to the 555
> output,
> and the base (with a suitable series resistor) as the new trigger input.
>
> Here's how it works. The 555 trigger is active low and the 555 output is
> active high. The transistor acts as an inverter so the base is now an
> active high trigger. So if we start from the idle state where the trigger
> input to the base is low and the output is low, the transistor is off and
> the 555 trigger is pulled up by the pullup resistor.
>
> Now you trigger the circuit by raising the base. The transistor turns on
> pulling the 555 trigger low, this triggers the 555, which raises the
> output
> high. So far so good.
>
> But remember that the emitter of the transistor is connected to the output
> of the 555. So when the output goes high it brings the emitter high too.
> Since there is no longer a voltage differential between the emitter and
> the
> base, the transistor turns off and the pullup pulls the trigger high
> again.
> And as long as the output of the 555 is high, that trigger cannot be
> pulled
> low. So you in theory can wiggle the base input as much as you like and it
> won't affect the timing of the 555.
>
> The only question is there any issue in terms of reverse breakdown of the
> transistor if the base is negative relative to the emitter? If there is
> an issue it possible to tie a reversed biased diode between the base and
> the emitter right? A quick look at a 2N2222 datasheet shows a emitter-base
> voltage of 6V. So presuming that we're working in a 5V system, no diode
> should be necessary.
>
> So if it all works there may be a winner here:
>
> 1. Use the 555 one shot output as the program clock for the PIC. There is
> no
> need to invert the signal as the bit is latched on the falling edge of the
> clock.
>
> 2. Since the new trigger is active high and with RS-232 the leading edge
> of
> the start bit is a transition from 1 (-12V) to 0 (12V) (i.e. a rising
> edge)
> you don't need to invert the TX signal, just condition it with a series
> resistor and a 4.7V or 5.1V zener. The output of that junction goes to the
> PIC program data PIC too in addition to the base of the trigger. Even
> better
> in the idle state both the clock and data pins to the PIC are low, so you
> can
> simply wire a switch from 13V to MCLR with a pulldown resistor to activate
> programming mode.
>
> 3. Now you tune the 555 delay to about 1/2 a character transmit time. This
> should be doable without any fancy equipment if you test with flip flop
> like the 74HCT74. Simply tie the transistor base to the D input of the FF
> and tie the output of the 555 to the clock (you may need to invert
> the signal). Then tune the delay resistor until when you send a 0x00 down
> the serial port you get one bit and when you send 0xff down the port you
> get the other bit.
>
> And that's it: a trivial serial PIC bootloader programmer that only uses
> the
> TX line and a handful of cheap plentiful components. And it should work
> with
> any USB to serial converter.
>
> Now it won't be fast. Presuming that you tune to something like 4800 or
> 2400
> BPS, it'll take awhile to program. To give you an idea Wouter's ZPL takes
> 70
> seconds to fill a 8K 18F part using the same technique. But it's really a
> one
> shot as you'll use it to program in a serial bootloader into the PIC and
> then
> the PIC can program itself directly from then on.
>
> The idea isn't new. As I said Wouter uses almost the exact same technique
> to
> implement his Zero Pin Programmer for the 18F series measuring the length
> of
> a transmitted character cell to transmit a bit. Also I'm sure that I've
> seen
> using a 555 to extract clock information from a serial stream somewhere or
> another.
>
> But it fits the bill exactly. Requires no intelligence. Works with any
> serial
> port. Doesn't require any modem control signals. Works with USB/serial
> converters. Uses cheap and plentiful parts. Finally I'm pretty sure that
> Wouter's ZPL Python software could be easily adapted into a programming
> base
> for the setup, so you wouldn't have to start writing the programming
> software
> >from scratch.
>
> Hope this helps. It's interesting enough that I think I may take an hour
> today to breadboard and do some tests.
>
> BAJ
>
> ---------------------------------------------------------------------
> To unsubscribe, e-mail: ####@####.####
> For additional commands, e-mail: ####@####.####
>
If a max232/max202 is present, then the 10v output can be used to put the
flash
device in high voltage programming mode. 9.2v is sufficient for activate the
HVP.
But only the maxim and the ex..., i don't remember exactly the replacement
company,
have parts, that have approximative 9.5V. The other manufacture uses diodes
and not
analog switches for the voltage double and don't reach the required
voltages.
And don't use the TX/RX pins. Even if there are handy, the hw layout
requires jumpers, or relays or separate cables.
Using the other pins, it's possible to use one or two jumpers connecting the
high
voltage using a standard serial cable.
I use a modified version of odyssey that use the serial port instead of the
parallel
one, and program the part without the tx/rx lines. Normally the tx/rx lines
is routed
to the rx/tx hw module on the pic.
And cheap usb to rs232 converter for less then 10 Euro exists.
The new 18f parts can reprogram the option location in low power programming
mode,
so using the 18f parts without voltage doubler is possible, annother
possibility is
to connect a dry 12V or a new 9V battery to the reset pins with only one
resistor
to protect the port, in the case the reset pin is set as output without
startup
delay, this for the 10f-16f parts.
--
+++ GMX - die erste Adresse für Mail, Message, More +++
1 GB Mailbox bereits in GMX FreeMail http://www.gmx.net/de/go/mail
