now drop the multiplex and get down to 3 wirws. .... Plus one for turning off the display and for PWMing. Right?
yes, SerIn, Clk, Stb, Enb

A typical sign of mine (16*108 color) will have about 650 of them. ... Are those 648 STs -as I guess- solderred on the same board containing LEDs? Then does it not suggest using two layer epoxy-glass boards?
The boards are 6 layers, it is difficult (impossible?) to route narrow wires on heavy copper, so there are 2 layers for LED power, 2 for signal one for logic power.

The 2221a has constant current outputs, thus no 8 resistors are required ... Adjusted for IMAX of LED with REXT? ... Okay Iout = ( Pd – VDD.IDD) / ( # outputs.Vo.Duty )
Ok, if you want to be picky, you save 7 resistors, not 8.


For a sign that size with a decent intensity he will need a 100A (8192 * 20mA = 164A) ... Uhum ... Got any suggestions except using some 8 PC power supplys? Of course I read this: ... change your design to have two power circuits one for the LEDs and one for the logic chips, it works in 1000 units built every month here.
My signs are modular, a board is e.g. 28 columns, in some cases I use 1 LED power supply, in some cases 2. I have no knbowledge of PC power supplies, I live in a 24V world.

While reading the I<OUT> vs. DutyCycle diagram of ST2221 (in a non-multiplexed display) is it Okay to consider the duty cycle to be some 90% provided that the needed time to hit strobe is short enough?
Hitting strobe is irrelevant. I do California sunshine with 20mA (Isn't non-mpx luvverly), thus no Iout problem.

A useable sign must adapt the intenity to ambient light .... You will want to sense ambient light and regulate your brightness. ... Using the REXT...no...by PWMing right? Controlled by an "eye" or what? I use a dirt cheap TI l/f converter and regulate intensity by PWM on OE.

I run my LEDs at approx 200kHz with no problems (need to for color) The problems we have had have all been related to ground bounce on the LED boards. Our current boards have two heavy copper layers for ground and one havy layer for VLED. One thing you MUST do is to have Vcc and Vled separated. .... Do I have to use "heavy copper" boards? It seems that this "Vcc and Vled separated" is a suggestion for that original poster's approach, since the VCC and VLED of ST2221 series is the same ... I mean impossible to separate.
The 2221 has NO Vled pin.

I seem to recall that in some countries multilayer boards are used by the board manufacturers for extorsion, try a european maker for the 6 layers.

Erik