Minsk: Document the registers

diff --git a/INSTRUCTIONS b/INSTRUCTIONS
index 62c8d95eb615b6f4fac76e41feecdb0556982491..7e3f8f078bfeeda75d5b9ba4219fdc365a2a9576 100644 (file)
--- a/INSTRUCTIONS
+++ b/INSTRUCTIONS
@@ -26,6 +26,17 @@ Data format:
                5 bits of exponent (2 decimal digits in BCD, the former one truncated to 1 bit)
 
 
+Registers:
+
+Minsk-2 has 3 registers:
+
+       accumulator     usually keeps the result of the previous arithmetic operation
+       R1              usually copies one of the operand of the instruction
+       R2              contains the value of acc
+
+(most programs use only the accumulator)
+
+
 Generic instruction format:  (by octal digits; some instructions deviate)
 
 sop mm xxxx yyyy