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Universal tritwise operations

Using OPA you can implement ANY 1-argument tritwise ternary function (there are 27 possibilities), for example:

 OPA NOP - no operation (N->N, O->O, P->P), but changing flag RSF based on value of register A
 OPA PON - invert value of register A (N->P, O->O, P->N) and flag RSF will be also inverted
 OPA OPN - tritwise rotate up register A (N->O, O->P, P->N) and set flag RSF
 OPA PNO - tritwise rotate down register A (N->P, O->N, P->O) and set flag RSF
 OPA NNN - write NNN to register A and set flag RSF to N
 OPA OOO - write OOO to register A and set flag RSF to O
 OPA PPP - write PPP to register A and set flag RSF to P

Using OPB you can implement ANY 2-argument tritwise ternary function (there are 19683 possibilities), for example:

 OPB NNN NOO NOP - perform operation MIN on A and B, save result to A and set flag RSF based on result
 OPB NOP OOP PPP - perform operation MAX on A and B, save result to A and set flag RSF based on result

Ternary conditional jump

To prepare 3 DP (data pointer) registers, we may use this code:

 LAI ONO - choose DPn 
 SAF - save A to F (DPF=N)
 LDI xxx xxx xxx - save 9-trit address to DPn
 LAI OOO - choose DPo
 SAF - save A to F (DPF=O)
 LDI yyy yyy yyy - save 9-trit address to DPo
 LAI OPO - choose DPp
 SAF - save A to F (DPF=P)
 LDI zzz zzz zzz - save 9-trit address to DPp

Then we may do conditional jump dependent on value of RSF:

 LAF - load A from F
 RRA - shift A right (move RSF value to DPF place)
 SAF - save A to F
 LPCD - load PC from chosen DP

Or we may do conditional jump dependent on value of BCF:

 LAF - load A from F
 RLA - shift A left (move BCF value to DPF place)
 SAF - save A to F
 LPCD - load PC from chosen DP

Simple subprogram call

Lets use DPo to save return pointer:

 LAI OOO
 SAF - set DPo as current DP
 LDI return_adr - save value of label "return_adr" to DPo
 JMP subprg_adr - call subprogram using label "subprg_adr"
return_adr:
 subprogram will return here

Then to return from subprogram by saved address we should do:

 LAI OOO - if DPF was changed during subprogram
 SAF - set DPo as current DP
 LPCD - load PC from DPo