LPC1788 SSP maximum speed

 LPC1788 SSP maximum speed

Hi
I have simple question about lpc1788:

*. what's the maximum bit rate of LPC1788 SSP?

maybe it's duplicated question but I need to be sure because I wanna buy and design new board and SSP bit rate is critical for me

more than 30Mbps is OK for me.

thanks in advance

 RE: LPC1788 SSP maximum speed

The CPSR divider needs to have a min value of 8 so with 120MHZ core clock you can get a max of 15MHz for the SSP clock.

Alex

 RE: LPC1788 SSP maximum speed

The theoretical value differs greatly from the maximum allowed by real-world hardware. Issues with trace length, buffers along the way of the signals etc. might limits signal propogation. I have just finished a simulator project that uses SSP1 of a LPC1768 at 100 MHz but the SSP bus is limited to 12.5 MHz.

 RE: LPC1788 SSP maximum speed

A max frequency limit may apply because of external factors like the PCB tracks you mention but you say that you have used a LPC1768 at 100 MHz but the SSP bus is limited to 12.5 MHz.

Why do you say limited, this is the max frequency based on specs for a core operating with 100MHZ, 100MHz/8=12.5MHz for the SSP clock

Alex

 RE: LPC1788 SSP maximum speed

In this case it is; I was trying to demonstrate the necessity to consider factors other than the software itself.

 RE: LPC1788 SSP maximum speed

Hi
in datasheet mentioned this number should be between 2-245 and even

where is "8"?

there is no any other fast serial protocol for lpc1788 about 30mbps or more?

I should connect it to spartan3 FPGA and this speed is awful. I don't have enough GPIO in FPGA and MCU and I must to transfer data between those, about 4MBps.

thanks a lot

 RE: LPC1788 SSP maximum speed

You are absolutely right , the minimum divider of 8 is the case for the SPI peripheral and not the SSP.

Note that a value of 255 is not possible because only even numbers should be used which means up to 254.

Alex

 RE: LPC1788 SSP maximum speed

;-(
So...!!!
which one is correct?
minimum=8 or 2

SPI or SSP can transmit up to what?

 RE: LPC1788 SSP maximum speed

SPI can transmit up to core_clock/8 and SSP core_clock/2.

Alex

 RE: LPC1788 SSP maximum speed

you mean LPC1788 on SSP can transmit up to 60Mbps without any limitation.

I knew I should observe a lot of things to make such a high speed connection about PCB design and etc but is it possible to gain more than 30mbps or IO pins can't toggle with such a speed (rising time and falling time or else doesn't limit these signals).

would you please do me a favor: config SSP to maximum speed and with Oscilloscope check it whether the signals are correct or have Distortion.

because I should select a powerful MCU with high speed SPI or SSP and if LPC1788 can satisfy me then I can buy it.

I'll appreciate you.

thanks

 RE: LPC1788 SSP maximum speed

Let me rephrase, according to the datasheet the max SSP clock is core_clock/2.

Even if it is possible to get such a rate externally it would not leave much cpu time to do anything that send spi.

Let me also add that in the following link it says
http://ics.nxp.com/support/faq/microcontrollers/lpc17xx/peripherals/

Q : What is the maximum SSP speed on the LPC17xx?
A : The maximum SSP speed (in master mode) is pclk/2. The maximum clock (CCLK) of the LPC17xx can be set to 100MHz and, since the peripheral clock (PCLK) can be equal to CCLK, the maximum SSP rate (master mode) will be 50 Mbit/sec (100MHz/2). In Slave mode, the SSP clock rate provided by the master must not exceed 1/12 of the SSP peripheral clock (selected in peripheral clock selection register). The content of the SSPnCPSR register is not relevant. So, the maximum SSP speed (in slave mode) will be 8Mbit/sec.

Alex

 RE: LPC1788 SSP maximum speed

thanks Alex , you are so fast to response
that's so good information

thanks thanks thanks