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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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 Posted: Fri Feb 27, 2009 4:37 pm |
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Look at this diagram in the 18F4550 data sheet.
| Quote: | | FIGURE 18-1: SPP DATA PATH |
It shows that all the following control signals are outputs.
| Quote: |
CK2SPP
OESPP
CSSPP
CK1SPP
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There is no way for another PIC (which is also a master-only)
to receive the clock, or the Output Enable (OESPP) signal.
I'm done with this. I can't help you any more. |
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urefowei
Joined: 21 Feb 2009
Posts: 10
Location: Philippines
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| Streaming Parallel Port |
| Posted: Sun Mar 01, 2009 2:39 pm |
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ckielstra, here's your post..
I know that SPP is master mode only,
how come you mentioned it there when the communication is PIC-to-PIC?
Please help..
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EcPaCo |
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Ttelmah
Guest
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| Re: Streaming Parallel Port |
| Posted: Sun Mar 01, 2009 3:40 pm |
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| urefowei wrote: | ckielstra, here's your post..
I know that SPP is master mode only,
how come you mentioned it there when the communication is PIC-to-PIC?
Please help..
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Because the heading of the thread asked about it?...
Best Wishes |
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urefowei
Joined: 21 Feb 2009
Posts: 10
Location: Philippines
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| Streaming parallel port |
| Posted: Sun Mar 01, 2009 3:59 pm |
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So you think its possible to communicate 2 PIC18F4550
through SPP??
Please help..
So the logic becomes one a master, and the other should be the slave..
Am I right about this??
But PCM think its not possible..
See the rest of the thread and please figure out..
We need your help..
If so, how can we make/configure the other PIC to become the slave??
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EcPaCo |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Sun Mar 01, 2009 6:27 pm |
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There are many options for inter device communications:
- SPI: serial, uses 3 wires + 1 select per device, max. speed = Fosc / (4 * 8) bytes per second
- I2C: serial, 2 wires, max. (official) speed = 400kHz / 8 = 250kbytes per second
- SPP: parallel, 11 wires, max. speed (from PCM's answer) = Fosc / 5 bytes per second
- Your own protocol: ... ???
You say you have used the SPI hardware already. Creating an SPI master driver in software is a piece of cake, just a for-loop clocking out the 8 bits and toggling the clock pin.
I've never used SPP but with the information given in the datasheet and in this thread it should be no problem to implement the master part. For the slave it is too bad Microchip didn't implement the hardware but it is easy to implement in software. Just poll the strobe line and when it goes active you read in the data. I wouldn't use interrupts for this because of the overhead involved.
As an alternative you might consider the USBwiz chipset from GHI Electronics which incorporates all your wished functionality: simultaneous access to two USB host ports and one SD card.
Just add a small processor, like the PIC, to tell this chipset what commands you want performed, for example to copy A to B. |
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urefowei
Joined: 21 Feb 2009
Posts: 10
Location: Philippines
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| Streaming parallel port |
| Posted: Mon Mar 02, 2009 1:31 am |
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| ckielstra wrote: | There are many options for inter device communications:
- SPI: serial, uses 3 wires + 1 select per device, max. speed = Fosc / (4 * 8) bytes per second
- I2C: serial, 2 wires, max. (official) speed = 400kHz / 8 = 250kbytes per second
- SPP: parallel, 11 wires, max. speed (from PCM's answer) = Fosc / 5 bytes per second
- Your own protocol: ... ???
You say you have used the SPI hardware already. Creating an SPI master driver in software is a piece of cake, just a for-loop clocking out the 8 bits and toggling the clock pin.
I've never used SPP but with the information given in the datasheet and in this thread it should be no problem to implement the master part. For the slave it is too bad Microchip didn't implement the hardware but it is easy to implement in software. Just poll the strobe line and when it goes active you read in the data. I wouldn't use interrupts for this because of the overhead involved.
As an alternative you might consider the USBwiz chipset from GHI Electronics which incorporates all your wished functionality: simultaneous access to two USB host ports and one SD card.
Just add a small processor, like the PIC, to tell this chipset what commands you want performed, for example to copy A to B. |
Assuming we have no alternative, What should we do??
What do you mean when you
| Quote: | | Just poll the strobe line and when it goes active you read in the data. I wouldn't use interrupts for this because of the overhead involved. |
How do you program this?
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EcPaCo |
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Posted: Wed Mar 04, 2009 6:03 pm |
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| Quote: | | Assuming we have no alternative, What should we do?? |
What you should do depends on many parameters that we don't know about.
- How many of these devices do you expect to produce?
- How much time do you have for this project?
- What experience does your team have?
- What throughput does your device require?
- etc.
You said you have 2 USB host controllers and 2 PIC processors. Your design will be easier and cheaper with only one controlling processor instead of two.
Transferring huge amounts of data as your application is going to do, is easier and faster when your processor has a lot of RAM. A PIC18 has a maximum of 4kb RAM, this might be sufficient but is tight.
How fast do you want to transfer the data?
I haven't checked, but let's say that a loop reading data from one 8-bit port and writing to another 8-bit port takes 5 instruction cycles.
With a maximum clock speed of 40MHz for most PIC18 processors this results in a maximum transfer speed of:
40MHz / (4 clocks per instruction * 5 instructions) = 2Mbyte/s
Copying a 700mB DIVX file will take close to 6 minutes. Not sure if your customers want to wait that long...
Somewhere you mentioned the use of SPI. Is this used for the data transfer? If yes, than your transfer speed will be 8 times slower.
If I had to do this project I would choose another processor. For example the NXP LPC2103 costs the same as your PIC18F4550 but has 8kb RAM compared to 2kb. If need arises there are other chips in the LPC210x family with RAM up to 64kB while the PIC18 family stops at a maximum of 4kb RAM.
And the processing speed is much higher (0.9 instruction / clock versus 0.25 instruction / clock for the PIC). An LPC2103 at 60MHz executes 54MIPS while a PIC at 40MHz reaches only 10MIPS.
Open source compilers for the ARM processor are available for free. |
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Guest
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| Posted: Thu Mar 05, 2009 11:29 am |
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I dont think we have time to change,
we just have to take the risk.
I hope we can do this |
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