The selected slave is addressed by a -Select line, so you need one output pin for each slave you want to talk to. So the number of free pins on your selected device limits the number of slaves you may talk to.
-SSelect * Number of slaves
Have a look into the SPIM datasheet, it explains everything quite clear.
If you used I2C to effect the approach the number of slaves allowed
would be governed by either / both the addressing mode and buss
C loading. 7 bit addressing would support 128 slaves if the buss loading
is within spec.
Of course I2C much slower than SPI.
If you elect to stay with SPI, slaves limited by pins available on PSOC
for chip select, unless you use chained mode. And higher buss speeds
imply shorter distances, unless you implement some type of LVDS
signaling. And of course you have paralled pins like clk on all slaves,
so buss C a factor for the speed you are trying to operate at.
Yes, it is possible to implement single master - multi slave system in PSoC1. Two normally used configurations for this are the Daisy chained multi slave system and parallel multislave system..
In Daisy chained multi slave system the output of one slave connects to the input of another and there is only one slave select line on the master end. To send the data to the nth slave in this case , the master must initiate n transactions. The number of slaves in this case is limited by the amount of delay acceptable in the design.
In parallel multi slave system , the slaves are connected in parallel and the master must provide separete slave select line for each slave. The number of slaves in this case is limited by the number of free pins available.
A detailed explanation on SPI working in PSoC1 can be found in AN51234.- http://www.cypress.com/?rID=34609
and the SPIM user module datasheet - http://www.cypress.com/?rID=3054