Hello,

I'm trying to implement something similar to this: 
http://hsm-aktuell.de/cnc-hr330.htm

I've disassembled one EPROM from the TNC155A cnc controller that reads 
the electronic handwheel but it's a bit tedious trying to figure out the 
protocol from that. I've managed to find out the baud rate, number of 
stop bits and parity settings from my disassembly and scoping the clk 
signal on the TNC155A board.

Would anyone have some info on the protocol for the Heidenhain 
electronic handwheel?

edit: Handwheel interfaces to the controller on the gfx board. There is 
TMS9995 cpu and a TMS9902 serial interface device. INT1 is used for 
character reception (5 bytes max or so it looks like)

1

INTR01 WP is at 0xdc00

2

3

INTR01 STCR *r1+,8

4

       SBO  18

5

       RTWP

From the disassembly listing I gathered that the serial interface runs 
at 38400 baud, one stop bit, even parity and 8-bits of data (TMS9902 
reset and setup code was easily found)

1

TMS9902RST LI   r12,>0000

2

           SBO  31

3

           LDCR @TMS9902_08,8

4

           SBZ  13

5

           LDCR @TMS9902_BC,12  

6

           MOV  r12,@>dc18  

7

           LI   r5,>0050  

8

           LI   r1,>dc04  

9

           MOV  r5,*r1+  

10

           CLR  *r1+  

11

           CLR  *r1+  

12

           CLR  *r1+  

13

           CLR  *r1+  

14

           MOV  r5,*r1+ 

15

           CLR  *r1+  

16

           CLR  *r1+ 

17

           CLR  *r1+ 

18

           CLR  *r1 

19

           LI   r5,>dc05

20

           MOV  r5,@>dc02 

21

           B    *r11

22

23

TMS9902_08 DATA >a300 ; TMS9902 %10100011 (1 stop bit even parity clk div by 3 8-bits) %00000000

24

TMS9902_BC DATA >000d ; TMS9902 LRDR register %00000000 %00001101 (((3MHz)/3)/13)/2 = 38461 baud