I am using the BCM53125S in a new product and i'm looking at the LED section of the design.
Reading the datasheet, it suggests that if the GMII interface is used then the parallel LED functionality (LED outputs directly driven from the BCM53125) is reduced from 20 possible displays to 10; I understand this as the GMII interface uses some if its lines for driving LEDs if this interface is not used.
It also states that the serial LED control bus (LEDDATA and LEDCLK) uses the same data source as the on-board parallel LED shift register drivers (Page 119 and Figure 47 of the Datasheet).
Can you confirm that this is correct?
I ask as my design is using both the GMII interface and the serial LED control bus and since the serial LED bus does not require the parallel LED drives present on the combined GMII / LED pins, is it not possible to configure / override the BCM53125S to output 20 LED displays over the serial LED bus or is it restricted to 10 as the datasheet says?
Also, can you confirm that it is indeed possible to display LED information for Port 5 (WAN / GMII Port) using the serial LED bus (the Datasheet seems to imply that this is indeed possible using the 'LED Function Map' and 'LED Enable Map' registers, but i'd just like to check as Port 5 is not available as a parallel LED output)?
Thanks in advance,
Please find the comment below per your two questions:
1. it's doable to use serial LED output 20 LED display (four LED display per port) even the strap pin GMII_LED_SEL=0 to select WAN port interface. The strap pin GMII_LED_SEL is just for parallel LED output.
2. For serial LED, it supports port0 ~ port5 LED display.
For parallel LED, it supports port0~port4 LED display.
Suggest please refer to our BCM953125RM reference schematic design and follow it, it's using serial LED output 20 LED display for port0~port5.
Anyway, hope this get through...
Thanks for your reply.
Understand that it is possible to display all 4 LED functions per port for 6 Ports in total (5 x GbE and 1 x WAN - Ports 0 to 5) using the Serial LED bus, regardless of the GMII_LED_SEL pin configuration setting - thanks for the clarification.
However, i'm still a little unsure regarding the structure of the output serial data and whether it is a variable length bitstream which is dependant on the Port LED functions enabled, or whether it is a fixed length bitstream regardless of the Port LED function settings, using padding bits for unused bits in the data.
For example, if i decide not to use all 4 LED displays for Ports 0 to 5 using the serial LED bus (total serial output bit length = 4 functions x 6 Ports = 24 bits), but want to use 2 LEDs per port instead, does the number of bits in the serial LED bitstream reduce by half (serial output bit length = 2 functions x 6 Ports = 12 bits) or does the bit length remain the same (24 bits, with unused bits 'padded out' in the serial data).
To put it more simply, does the serial LED bus output bitstream contain ONLY the LED functions that have been enabled and is therefore variable in length, or is it a fixed length output with padding bits included for any unused LED functions?
For serial LED, it is not fixed length with padding bits. And it can program the LED bits for each port, up to 4 bits maximum.
The LED display are configured by LED Function 0/1 Control Register
For example, if you assign only 2 LED functions and will see LED display for next port at every 2 LEDs (i.e. you do not have to reserve/design 4 shift registers per port, if you are not using All 4 LED displays.)
Suggest to have schematic review when your schematic design is completed, please contact your local distributor and submit CSP case for schematic review then.
Thanks for your reply... i understand now.