SPI bus - SCK pin activity on pin 13 (LED)

Using Arduino Programming Questions
#1

am wondering what sort of activity (frequency of high & low) is happening on the Clock pin when the SPI bus is active.
since it's on Pin 13, one can see the LED flash when it's active.

i am troubleshooting using an ENC28J60 module on the SPI bus and i noticed the LED is staying on - or maybe flashing very fast because it's not as bright as when it's "fully HIGH".

is it normal for Ethernet activity to 'pulse' the Clock pin like that ?

i tried to observe an SD Card module on the same SPI bus and the LED only blinked a few times and then stayed off.

is there something not right happening on the SPI bus if the LED is "constantly on" ?

#2

The clock signal is used whenever the SPI bus is active. How active that bus is depends on the code that's using the bus. I would imagine the ENC28J60 is being polled for data on a regular basis, so the SPI bus is being used a huge amount (i.e., pretty much constantly).

#3

majenko:
…
I would imagine the ENC28J60 is being polled for data on a regular basis, so the SPI bus is being used a huge amount (i.e., pretty much constantly).

or if it’s hanged ?
what would be a cause for the code to hang <here> ?

  Serial.println("\n[backSoon]");
                                [color=teal]<here>[/color]  
  if (ether.begin(sizeof Ethernet::buffer, mymac) == 0) 
    Serial.println( "Failed to access Ethernet controller");

full code as follows;

  // ##############################
 // copy direct from backSoon-ino #
// ################################

// Present a "Will be back soon web page", as stand-in webserver.
// 2011-01-30 <jc@wippler.nl> http://opensource.org/licenses/mit-license.php
 
#include <EtherCard.h>

#define STATIC 0  // set to 1 to disable DHCP (adjust myip/gwip values below)

#if STATIC
// ethernet interface ip address
static byte myip[] = { 192,168,1,7 };  
                    // NOT showing in DCHP Active IP table ?
                     // just pick one NOT currently in use
// gateway ip address
static byte gwip[] = { 192,168,1,1 };
#endif

// ethernet mac address - must be unique on your network
static byte mymac[] = { 0x02,0xDD,0xDD,0x00,0x00,0x01 };
                      
byte Ethernet::buffer[500]; // tcp/ip send and receive buffer

char page[] PROGMEM =
"HTTP/1.0 503 Service Unavailable\r\n"
"Content-Type: text/html\r\n"
"Retry-After: 600\r\n"
"\r\n"
"<html>"
  "<head><title>"
    "Service Temporarily Unavailable"
  "</title></head>"
  "<body>"
    "<h3>This service is currently unavailable</h3>"
    "<p><em>"
      "The main server is currently off-line.
"
      "Please try again later."
    "</em></p>"
  "</body>"
"</html>"
;

void setup(){
  Serial.begin(9600);
  Serial.println("\n[backSoon]");
                         <here>  
  if (ether.begin(sizeof Ethernet::buffer, mymac) == 0) 
    Serial.println( "Failed to access Ethernet controller");
#if STATIC
  ether.staticSetup(myip, gwip);
#else
  if (!ether.dhcpSetup())
    Serial.println("DHCP failed");
#endif

  ether.printIp("IP:  ", ether.myip);
  ether.printIp("GW:  ", ether.gwip);  
  ether.printIp("DNS: ", ether.dnsip);  
}

void loop(){
  // wait for an incoming TCP packet, but ignore its contents
  if (ether.packetLoop(ether.packetReceive())) {
    memcpy_P(ether.tcpOffset(), page, sizeof page);
    ether.httpServerReply(sizeof page - 1);
  }
}
#4

Taking a long time to get DHCP maybe?

#5

majenko:
Taking a long time to get DHCP maybe?

hmm, now that's a thought !
i haven't yet tried disabling it.
there's no timeout (i think) in the code - so it just hangs there and not even entering the "error-trap"(?)

that's a possible "What" but it doesn't cover the "Why" which is the main problem i'm having.

could an insufficient power supply issue be a possible cause for the "no response" - from the router back to the module ?
(i've just been reading these cables carry about 2.5 V which should be covered by the 3.3V of the module ?)

#6