readme.html: Fixed link to Po Drátě

[minsk.git] / INSTRUCTIONS

diff --git a/INSTRUCTIONS b/INSTRUCTIONS
index e1a6c54277c17226a787bdd9b738569960f4cb9e..b1a4e866d07d90c1900f4dfc44cd7e74b85ddb90 100644 (file)
--- a/INSTRUCTIONS
+++ b/INSTRUCTIONS
@@ -1,11 +1,13 @@
-MINSK-2 INSTRUCTION SET
-~~~~~~~~~~~~~~~~~~~~~~~
+MINSK-2/MINSK-22 INSTRUCTION SET
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 Data format:
 
 Data format:
 

-       The memory of the machine consists of 4096 37-bit words (the topmost bit
+       The memory of the Minsk-2 machine consists of 4096 37-bit words (the topmost bit

        is always used as a sign). The 0th memory cell is hard-wired to 0, writes
        have no effect.
 
        is always used as a sign). The 0th memory cell is hard-wired to 0, writes
        have no effect.
 

+       The Minsk-22 machine has 2 banks of 4096 37-bit words each.
+

        Fixed-point numbers: sign and 36 significant bits
 
        Binary floating-point numbers (from top to bottom bit):
        Fixed-point numbers: sign and 36 significant bits
 
        Binary floating-point numbers (from top to bottom bit):


@@ -28,7 +30,7 @@ Data format:
 
 Registers:
 
 
 Registers:
 

-Minsk-2 has 3 registers:
+Minsk-2/Minsk-22 has 3 registers:

 
        accumulator     usually keeps the result of the previous arithmetic operation
        R1              usually copies one of the operand of the instruction
 
        accumulator     usually keeps the result of the previous arithmetic operation
        R1              usually copies one of the operand of the instruction


@@ -53,7 +55,26 @@ Indexing mode bits:
    |   |
    |   +---- index register: when non-zero, lower 12 bits of the memory
    |         cell #iiii are added to yyyy, next 12 bits are added to xxxx
    |   |
    |   +---- index register: when non-zero, lower 12 bits of the memory
    |         cell #iiii are added to yyyy, next 12 bits are added to xxxx

-   +----- address extension (supported only on Minsk-22, not in our Minsk-2)
+   +----- address extension (supported only on Minsk-22)
+
+
+Address extension:
+
+       In Minsk-22 mode, the address extension bits can be used to access the second
+       bank of memory in the machine. Each of the bits selects the memory bank 
+       (either 0 or 1) that one of the operands operate on:
+        
+               The first (high) bit selects the memory bank for operand1 (x)
+               The second (low) bit selects the memory bank for operand2 (y)
+
+       The instruction pointer always operates on bank 0. This extends to situations 
+       where a (jump) instruction sets the instruction pointer to either x or y; the 
+       address extension bits are effectively ignored in those cases.
+
+       Similarly, the indexing word is always read from bank 0.
+
+       In Minsk-2 mode, setting the address extension bits to anything but 0 is an
+       error in all cases.

 
 
 For arithmetic instructions, the lower 2 bits of <sop> encode addressing mode:
 
 
 For arithmetic instructions, the lower 2 bits of <sop> encode addressing mode: