6502

6502 page on Wikipedia
6502 page on CPU-World

Pinout (DIP40)

        +--\/--+
    Vss | 1  40| *RES
    RDY | 2  39| /2 (out) (clock internal?)
/1(out) | 3  38| S0
   *IRQ | 4  37| /0 (in) (clock external?)
     NC | 5  36| NC
   *NMI | 6  35| NC
   SYNC | 7  34| R/*W
 +5 Vcc | 8  33| D0
     A0 | 9  32| D1
     A1 |10  31| D2
     A2 |11  30| D3
     A3 |12  29| D4
     A4 |13  28| D5
     A5 |14  27| D6
     A6 |15  26| D7
     A7 |16  25| A15
     A8 |17  24| A14
     A9 |18  23| A13
    A10 |19  22| A12
    A11 |20  21| Vss
        +------+

Frequency: set reader to FREQ, put black probe to GND, red probe to 37 or 39 to measure CPU clock
Guru's comment: 37(in), 3 & 39 (out)