How you directly access serially chained devices, like LEDS, shift registers, etc?

[richard]

With APA102C, 1 shiftout statement updates color of 1 pixel (3 leds )
In case of HT16K33, 3 shiftout statement will update color of 8 pixels (24 leds), so resulting speed will be 8/3=2.6 times higher.

apa102 16million colours, 32 level global power control
HT16K33 8 colours no power control

dmd panels come in p2.5 p3 etc to p10 the number is the pixel grid spacing in mm
dmd panels are just shift registers multiplexed in 4 row pair strings there is no controller as such

if you want the complexity of colour and power level control on a per pixel basis you need to store and transfer
the info to represent it, there is no simple

[CuriousOne]

ht16k33 was just an example, note the "or similar" in my post - I don't exactly remember which holtek chip has individual brightness control, but there are some, they're installed in these commercial color rgb panels.

Yes, 2.5mm spacing, that is huge in 2.5 x 2.5 mm area, where you will have 4 RGB pixels, with SMT leds, you can have 3x3 or even 4x4 RGB pixels.

[HenrikOlsson]

Since the LEDs effectively ARE shift registers daisychained together there is no way to update a single LED, you doneed to refresh the complete string. But if you design a 192x12 display you could, for example have 12 separate strings of 192 leds so that you could update the display row by row - if that helps.

You'll need a PIC with lots of RAM though, 192x12x3=6912 bytes to hold the display data.

And, since you talk about efficiency, forget SHIFTOUT and start using the MSSP module or the SPI module on the newer PICs instead.

[richard]

192x12x3=6912 bits == 864 bytes

[CuriousOne]

Each color value is 8 bit, so it is 6912 bytes, not bits But that's ok, I'll use external EEPROM as display buffer.
MSSP would be great, but no PBP support as far as I know - need to use ASM....

[richard]

it would be difficult to pack rgb leds more tightly than these
p3 64x64 p4 32x64 modules




and they work, limited to 8 colours with pbp

[CuriousOne]

Yes, bottom ones are 3030 leds. And they're placed sparsely.
Now check footprint of 1206 or 0805 enclosure and compare sizes

[HenrikOlsson]

Each color value is 8 bit, so it is 6912 bytes, not bits But that's ok, I'll use external EEPROM as display buffer.
MSSP would be great, but no PBP support as far as I know - need to use ASM....

Say what? You start the thread about efficiency and then you're going to use external memory as display buffer?

There is zero need for any assembly code to operate the MMSP module (or the SPI module on the Q devices for that matter).

[tumbleweed]

If you just need more RAM for a display buffer there are much faster devices than an external EEPROM, like the 23LC512 serial SPI SRAM.
Also, since SHIFTOUT runs at approx 50KHz, you could even write your own dedicated version that would be MUCH faster than that, although using the MSSP/SPI peripheral is pretty straight forward and would easily get you into the multi-MHz range.