From 1d35f659ee074af723a5ff73fe28e50d7e6aafbd Mon Sep 17 00:00:00 2001
From: n loewen <nick@nloewen.com>
Date: Wed, 23 Aug 2023 14:45:14 +0100
Subject: [PATCH] readme - WIP - Change "Instruction Set" section to describe a
 new, revised architecture

---
 readme.md | 79 +++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 57 insertions(+), 22 deletions(-)

diff --git a/readme.md b/readme.md
index 8a1d752..8e6e877 100644
--- a/readme.md
+++ b/readme.md
@@ -32,28 +32,6 @@ With single stepping + pretty-printed display:
 With single stepping + verbose debugging output:  
 ```./run-cpu stepdebug source_code.asm```
 
-## Instruction set
-
-    00   END
-    01   STO lit#   ; store ... mem[lit#] <- A
-    02   STO addr   ; store ... mem[mem[addr]] <- A
-    03   LDA lit#   ; load  ... A <- lit#
-    04   LDA addr   ; load  ... A <- mem[addr]
-    05   ADD lit#   ; add   ... A <- A + lit#      ... and un/set carry flag
-    06   ADD addr   ; add   ... A <- A + mem[addr] ... and un/set carry flag
-    07   SUB lit#   ; sub   ... A <- A - lit#      ... and un/set carry flag
-    08   SUB addr   ; sub   ... A <- A - mem[addr] ... and un/set carry flag
-    09   HOP lit#   ; hop   ... skip next instruction if A == lit# ... when true: IP <- PC + 4
-    0A   HOP addr   ; hop   ... skip next instruction if A == addr ... when true: IP <- PC + 4
-    0B   JMP lit#   ; jump  ... IP <- lit#
-    0C   JMP addr   ; jump  ... IP <- addr
-    0D   FTG lit#   ; toggle flag by number (see details below)
-    0E   FHP lit#   ; flag hop ... skip next instruction if flag is set ... when true: IP <- PC + 4
-    0F   NOP ————   ; no operation
-
-- Instructions are two bytes long:
-  one byte for the opcode, one for the operand    
-
 
 ## Registers and Flags
 
@@ -67,6 +45,63 @@ With single stepping + verbose debugging output:
           C = 0
     - (bitwise, `0000 = NZOC`)
 
+
+## Instruction set
+
+### Operations
+
+```
+Hex  Mnem.  Name         Operand type  Effect
+---------------------------------------------
+
+00   END    End          (ignored)     Halt CPU
+01   NOP    No op        (ignored)     None
+
+50   STO    Store        literal #     mem[lit#] = A
+51   LDA    Load         literal #     A = lit#
+52   ADD    Add          literal #     A = A + lit#
+53   SUB    Sub          literal #     A = A - lit#
+54   HOP    Hop          literal #     If A == lit#, skip next op (IP += 4)
+55   JMP    Jump         literal #     IP = lit#
+56   FTG    Flag toggle  literal #     Toggle flag, where flag number == lit#
+57   FHP    Flag hop     literal #     Skip next op if flag is set, where flag number == lit#
+
+60   STO    Store        address       mem[mem[addr]] = A
+61   LDA    Load         address       A = addr
+62   ADD    Add          address       A = A + mem[addr]
+63   SUB    Sub          address       A = A - mem[addr]
+64   HOP    Hop          address       If A == mem[addr], skip next instruction (IP += 4)
+65   JMP    Jump         address       IP = mem[addr]
+```
+
+### Map + effects on flags, registers
+
+```
+hex   bin          group  mode      op   mem  flags  IP
+-------------------------------------------------------
+00    0000 0000    0      --        END              +2
+01    0000 0001    0      --        NOP              +2
+
+50    0101 0000    1      direct    STO  w           +2
+51    0101 0001    1      direct    LDA  r    NZ     +2
+52    0101 0010    1      direct    ADD       NZOC   +2
+53    0101 0011    1      direct    SUB       NZOC   +2
+54    0101 0100    1      direct    HOP              +2/+4
+55    0101 0101    1      direct    JMP              arg
+56    0101 0110    1      direct    FTG       NZOC   +2
+57    0101 0111    1      direct    FHP       NZOC   +2/+4
+
+60    0110 0000    1      indirect  STO  r,w         +2
+61    0110 0001    1      indirect  LDA  r,r  NZ     +2
+62    0110 0010    1      indirect  ADD  r    NZOC   +2
+63    0110 0011    1      indirect  SUB  r    NZOC   +2
+64    0110 0100    1      indirect  HOP  r           +2/+4
+65    0110 0101    1      indirect  JMP  r           arg
+66    0110 0110    1      indirect  FTG  r    NZOC   +2
+67    0110 0111    1      indirect  FHP  r    NZOC   +2/+4
+```
+
+
 ## CPU start-up
 
 When starting up, the CPU executes a `JMP $FF`.