Default is 1 mac in the table.

To allow a hub, but not let the other talk on the switch port other than 1212.1212.1212:

S5#sh run int fa 0/22
Building configuration...

Current configuration : 182 bytes
!
interface FastEthernet0/22
 switchport mode access
 switchport port-security
 switchport port-security violation restrict
 switchport port-security mac-address 1212.1212.1212
end

S5#