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--- en:multiasm:piot:chapter_4_3 [2026/01/19 10:52] – marcin
+++ en:multiasm:piot:chapter_4_3 [2026/01/19 15:08] (current) – marcin
@@ Line 10: / Line 10: @@
 **R16-R31:**
 General-purpose registers that can be used with immediate
+Comparison Table: AVR Registers R0–R15 vs. R16–R31
+^  Feature                     ^  R0–R15                                                            ^  R16–R31                                        ^
+|  Instruction compatibility   |  Cannot be used with immediate instructions (LDI, CPI, ORI, ANDI)  |  Fully compatible with immediate instructions   |
+|  Opcode encoding             |  Not encodable in 4‑bit register fields                            |  Encodable in all immediate‑type formats        |
+|  Typical compiler usage      |  Less preferred; used for temporary or special roles               |  Preferred for arithmetic and logic operations  |
+|  Special-purpose roles       |  R0: scratch<br>R1: constant zero                                  |  R26–R31 used as X/Y/Z pointer registers        |
+|  Pointer support             |  No                                                                |  Yes: X, Y, Z pointers                          |
+|  Efficiency                  |  Less efficient for immediate operations                           |  More efficient due to shorter opcodes          |
+|  Multiplication involvement  |  R0/R1 used implicitly for results                                 |  Not used by multipliers                        |
+|  Suitability in ASM          |  Limited; avoid with immediates; R0/R1 have special rules          |  Recommended for general ALU operations         |
+|  GCC policy                  |  R1 must remain 0; R0 is volatile                                  |  Treated as normal general-purpose registers    |
 <figure avr_registers>
-{{en:multiasm:piot:avr_register1.svg?800|AVR Registers}}
+{{en:multiasm:piot:avr_register1.svg?300|AVR Registers}}
 <caption>AVR Registers</caption>
 </figure>
@@ Line 22: / Line 35: @@
 <figure avr_registers>
-{{en:multiasm:piot:x_y_z_registers.svg?800|Extended registers}}
+{{en:multiasm:piot:x_y_z_registers.svg?400|Extended registers}}
 <caption>Etended Registers</caption>
 </figure>
@@ Line 35: / Line 48: @@
 <table Register properties>
 <caption>Register properties</caption>
-^ Register ^ Purpose ^ Combined With ^ Enables ^
+^  Register  ^  Purpose                              ^  Combined With  ^  Enables                                           ^
-| RAMPX	| Extends data addressing | X register | Access to data above 64 KB using X |
+|  RAMPX     |  Extends data addressing              |  X register     |  Access to data above 64 KB using X                |
-| RAMPY | Extends data addressing | Y register | Access to data above 64 KB using Y |
+|  RAMPY     |  Extends data addressing              |  Y register     |  Access to data above 64 KB using Y                |
-| RAMPZ | Extends data and program addressing |Z register| Access to data and constants above 64 KB using Z |
+|  RAMPZ     |  Extends data and program addressing  |  Z register     |  Access to data and constants above 64 KB using Z  |
-| RAMPD | Extends data addressing | Z register | Direct access to data above 64 KB |
+|  RAMPD     |  Extends data addressing              |  Z register     |  Direct access to data above 64 KB                 |
-| EIND | Extends program addressing | Z register | Jumps and calls to program memory above 128 KB |
+|  EIND      |  Extends program addressing           |  Z register     |  Jumps and calls to program memory above 128 KB    |
 </table>

en/multiasm/piot/chapter_4_3.1768812766.txt.gz · Last modified: 2026/01/19 10:52 by marcin