(Sourced from the Ultimate MSX FAQ) (Giovanni R. Nunes)

Female 50 pin connector

 1:/CS1          2:/CS2
 3:/CS12         4:/SLTSL
 5: RSV(N.C)     6:/RFSH
 7:/WAIT         8:/INT 
 9:/M1          10:/BUSDIR
11:/IORQ        12:/MERQ  
13:/WR          14:/RD    
15:/RESET       16: RSV(N.C)
17: A 9         18: A15               
19: A11         20: A10               
21: A 7         22: A 6               
23: A12         24: A 8                 
5: A14         26: A13               
27: A 1         28: A 0               
29: A 3         30: A 2               
31: A 5         32: A 4               
33: D 1         34: D 0               
35: D 3         36: D 2               
37: D 5         38: D 4               
39: D 7         40: D 6               
41: GND         42: CLOCK             
43: GND         44: SW1               
45: +5V         46: SW2               
47: +5V         48: +12V              
49: SOUNDIN     50: -12V            
                                     

Short description of the pins: (from Philips VG8235 manual)

1-ROM addresses 4000-7FFF select signal

2-ROM addresses 8000-BFFF select signal

3-ROM addresses 4000-BFFF select signal (for 256k ROM)

4-Slot select signal

5-Reserved signal line - use inhibited

6-Refresh cycle signal

7-CPU's WAIT request signal

8-Interrupt request signal to CPU

9-Signal expressing CPU fetch cycle

10-This signal controls direction of external databus buffer. Cartridges are selected and L level is output from each cartridge at data transmission time

11-I/O request signal

12-Memory request signal

13-Write timing signal

14-Read timing signal

15-System reset signal

16-Reserved signal line - use inhibited

17-32-Address bus signals

33-40-Data bus signals

41-Signal ground

42-CPU clock 3.579545MHz

43-Signal ground

44,46-For insertion/removal protect

45,47- +5V power source

48- +12V power source

49-Sound input signal (-5bdm)

50- -12V power source