As you probably know, DSP n where n is one of the digit keys [0] to [9] sets the display precision. E.g. DSP 2 in FIXed mode gives you “0.00”, DSP 3 gives “0.000”.
Here’s how the internals do that
Pressing [DSP] gives
00214 ... 00217 keys to a ; A= 0000fffffff920 (scanrow=9 scancol=2) 00256 a -> rom address ; 5*9+2=47 =057 01457 if n/c go to 01510 ; part of a "jump table". ; do [DSP]: ; set s 13 and M1[x]=060 01510 jsb 01740 ; [DSP] is a prefix key, clear prefix state 01511 load constant 6 ; C= 00000000000060 P= 0 00451 1 -> s 13 ; S= .........9...d.f 00144 m1 exch c ; C= 03000000000400 M1=00000000000060 ... (update display and back into wait loop)
Pressing [0] gives
00214 ... 00217 keys to a ; A= 0000fffffff720 (row 7 col 2) 00256 a -> rom address ; 5*7+2=37 =045, C= 00000000000060 P= 1 01445 if n/c go to 01613 ; do [0]: 01613 if 1 = s 4 : 01614 then go to 01654 01615 if 0 = s 6 : 01616 then go to 01643 01643 if 0 = s 8 : 01644 then go to 01654 01654 if c[p] # 0 01655 then go to 01566 01566 delayed rom 01 01567 if n/c go to 0437 00437 ...; A= 00000000000060 M1=00000000000060 S= .........9.....f C= 00000000000000 P= 12 06027 a -> rom address ; A[2,1]= 0x06 = 0000 0110 = 00 000 110 = 006 06006 if n/c go to 06040 ; do [DSP] n (or the other 0x6[a-f] hex codes) ; check n < 10 else go elsewhere ; get display info etc from ram[62] ; shift A left by 6 so A[0] lines up with dsp nibble in ram[62] ; put n in the dsp nibble then save back to ram[62] 06040 ... ; S= ......6..9.....f A= 00000000000060 C= 0000000000000a P= 0 07460 if a >= c[p] ; check n < 10 (A= 0...6n) 07461 then go to 07413 07462 jsb 07706 ; select ram bank 3, P= 0 C= 00000000000000 07463 data register -> c 14 ; ram[62] -> C= 00000012220000 ; shift A left by 6 07464 p <- 6 ; P= 6 07465 load constant 5 ; C= 00000015220000 P= 5 07466 p <- 6 ; P= 6 07467 shift left a[w] ; A= 00000000000600 07470 c - 1 -> c[p] ; C= 00000014220000 07471 if n/c go to 07467 ; A= 00000000006000 C= 00000013220000 ; A= 00000000060000 C= 00000012220000 ; A= 00000000600000 C= 00000011220000 ; A= 00000006000000 C= 00000010220000 ; A= 00000060000000 C= 0000001f220000 07471 if n/c go to 07467 ; put n in the dsp nibble 07472 a exchange c[p] ; A= 0000006f000000 C= 00000010220000 ; save the updated DSP setting 07473 c -> data register 14 ; c= 00000010220000 -> ram[62] 07474 delayed rom 00 07475 if n/c go to 0114 ... (update display and back into wait loop) ; "0."
The same for [DSP] [3] ends like this:
; [3] pressed 00214 ... 00217 keys to a ; A= 00fffffffff600 00256 a -> rom address ; 5*6+0=30 = 036, A= 00fffffffff1e0 P= 1 C= 00000000000060 M1=03000000000400 ; [0] was to 01445 then 01613 - gave C=0...060 01436 c + 1 -> c[x] ; C= 00000000000061 01437 c + 1 -> c[x] ; C= 00000000000062 01440 if n/c go to 01612 01612 c + 1 -> c[x] ; C= 00000000000063 ; now have C=0...060 - 0...069 for DSP 0-9. This is the hex code for DSP 0-9 01613 if 1 = s 4 : 01614 then go to 01654 01615 if 0 = s 6 : 01616 then go to 01643 01643 if 0 = s 8 : 01644 then go to 01654 01654 if c[p] # 0 01655 then go to 01566 01566 delayed rom 01 01567 if n/c go to 0437 00437 ... ; A= 00000000000063 M1=00000000000063 S= .........9.....f C= 00000000000000 P= 12 06027 a -> rom address ; A[2,1]= 0x06 = 0000 0110 = 00 000 110 = 006 06006 if n/c go to 06040 ; all of the 0x60-0x6f hex codes go here. ; do [DSP] n (or the other 0x6[a-f] hex codes) 06040 ... ; S= ......6..9.....f 07463 data register -> c 14 ; ram[62] -> C= 00000010220000 ; shift A[0] left 6 positions so it lines up with the DSP nibble in C[6] 07464 ... ; A= 00000000000630 C= 00000014220000 ; A= 00000000006300 C= 00000013220000 ; A= 00000000063000 C= 00000012220000 ; A= 00000000630000 C= 00000011220000 ; A= 00000006300000 C= 00000010220000 ; A= 00000063000000 C= 0000001f220000 07471 if n/c go to 07467 ; put the new DSP n value into C 07472 a exchange c[p] ; A= 0000006f000000 C= 00000013220000 ; save the updated value 07473 c -> data register 14 ; C (=00000013220000) -> ram[62] 07474 delayed rom 00 07475 if n/c go to 0114 ... (update display and back into wait loop) ; "0.000"
More info is in 67-dsp-0.txt.
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