Model 100 Option ROM pinout

M100     Desc.   27C256 28C256 28F256
Molex          dip/soic plcc32 plcc32

 1       Vcc     28,1   32,31  32
 2       A10     21     24     23
 3       A7       3      4      5
 4       A6       4      5      6
 5       A5       5      6      7
 6       A4       6      7      8
 7       A3       7      8      9
 8       A2       8      9     10
 9       A1       9     10     11
10       A0      10     11     12
11       D0      11     13     13
12       D1      12     14     14
13       D2      13     15     15
14       GND     14     16     1,16
15       D3      15     18     17
16       D4      16     19     18
17       D5      17     20     19
18       D6      18     21     20
19       D7      19     22     21
20       A11     23     27     25
21       OE_     22     25     24
22       A13     26     30     28
23       NC
24       A12      2      3      4
25       A9      24     28     26
26       A8      25     29     27
27       CE_     20     23     22
28       A14     27      2     29

To read/dump a commercial option rom in a programmer, tell the programmer software the chip is a 27C256 DIP28, and connect programmer pin 28 to option rom pin 1, and leave programmer pin 28 unconnected.

Sample command line for "minipro" on linux, use with a TL866 programmer:

   sudo minipro -y -p "27C256 @DIP28" -r myrom.bin

That will read the chip and write the contents to a file named myrom.bin