Just a couple of commands to show the ASIC/port mapping on most cisco switches.

show interfaces capabilities module

Is used on smaller switches e.g. 3750

m00nie-C3750#show platform pm if-numbers

interface gid  gpn  lpn  port slot unit slun port-type lpn-idb gpn-idb
----------------------------------------------------------------------
Gi1/0/1   1    1    1    1/3  1    1    1    local     Yes     Yes
Gi1/0/2   2    2    2    1/0  1    2    2    local     Yes     Yes
Gi1/0/3   3    3    3    1/1  1    3    3    local     Yes     Yes
Gi1/0/4   4    4    4    1/2  1    4    4    local     Yes     Yes
Gi1/0/5   5    5    5    0/2  1    5    5    local     Yes     Yes
Gi1/0/6   6    6    6    0/3  1    6    6    local     Yes     Yes
Gi1/0/7   7    7    7    0/0  1    7    7    local     Yes     Yes
Gi1/0/8   8    8    8    0/1  1    8    8    local     Yes     Yes
Gi1/0/9   9    9    9    3/3  1    9    9    local     Yes     Yes
Gi1/0/10  10   10   10   3/0  1    10   10   local     Yes     Yes
Gi1/0/11  11   11   11   3/1  1    11   11   local     Yes     Yes
Gi1/0/12  12   12   12   3/2  1    12   12   local     Yes     Yes

Is this out the ASIC used by the port is under the "port" column (doesnt display very well here). So for example Gi1/0/1 uses ASIC 1 port 3 and Gi1/0/10 uses ASIC 3 port 0.

On 6500s the command is
show interfaces capabilities module
E.g

m00nie-C6509#show interfaces capabilities module 1

GigabitEthernet1/1
Dot1x:                 yes
Model:                 WS-X6724-SFP
Type:                  1000BaseSX
Speed:                 1000
Duplex:                full
Trunk encap. type:     802.1Q,ISL
Trunk mode:            on,off,desirable,nonegotiate
Channel:               yes
Broadcast suppression: percentage(0-100)
Flowcontrol:           rx-(off,on,desired),tx-(off,on,desired)
Membership:            static
Fast Start:            yes
QOS scheduling:        rx-(1q8t), tx-(1p3q8t)
CoS rewrite:           yes
ToS rewrite:           yes
Inline power:          no
SPAN:                  source/destination
UDLD                   yes
Link Debounce:         yes
Link Debounce Time:    yes
Ports on ASIC:         1-12   <---------- [ASIC HERE!!!!]
Port-Security:         yes

The output here is more obvious with the "Ports on ASIC" showing the actual port numbers used/shared by the ASIC.

m00nie :)