Ferranti Mark 1 Instruction Codes

This page gives a summary of the instruction codes, first in logical order then in numerical order. In between is a key for the notation used. The 6-bit function codes are specified using the Base-32 notation used in the Programmer's Handbook (which go up from 0, 1, 2, 3, ... 63 in the form //, T/, /E, TE, ... T£ -- see note 3 for the Handbook). The link from the base-32 code goes to the appropriate part of the Handbook, although for many of the arithmetic codes there is no explicit specification, so the link is merely to the table of arithmetic instructions in the Handbook text.

The notation used in both summaries is that of the Handbook; the list in numerical order is essentially a copy of the text contained in the Handbook's appendix.

Note that the ' symbol is simply used to indicate a value that is reset by the instruction.

Summary Instruction Code (ordered logically)

Arithmetic Instructions							(Key)
T½		A' = S±		T:		A' = 0
T/		A' = S+		TF		A' = -S±
/S		S' = L		TK		A' = 2S±
TC		A' = A + S±		/E		S' = M
TI		A' = A + S+		/A		S' = M, M' = 0
TN		A' = A - S±		TA		S' = L, A' = 0
/K		D' = S±		/U		S' = L, L' = M, M' = 0
/C		D' = S+		/J		M' = M + S
/F		A' = A + D S±		/I		L' = M, M' = L
/N		A' = A + D S+		TR		A' = A and S±
/D		A' = A - D S±		TD		A' = A or S±
/½		A' = A - D S+		TJ		A' = A neq S±
				/@		standardise
B-line Instructions						Control Instructions
TT		B' = s		/P		Uncond. direct jump
TL		B' = B - s		/Q		Uncond. rel. jump
TZ		s' = B		/H		A-cond. direct jump
TO		# B' = s		/M		A-cond. rel. jump
TG		# B' = B - s		/T		B-cond. direct jump
TB		# s' = B		/O		B-cond. rel. jump
				/G		Stop if /G switch set
Miscellaneous				/L		Stop if /L switch set
/:		S as mag. instr.
//		H as mag. instr.
/Z		S' = H
/W		Random number generator
/R		Sideways adder
/V		Hoot
T£		# Dummy

• Direct Jump -- In conventional parlance this is an indirect jump, i.e. the destination address is held in a store word rather than in a field of the instruction itself (see note 8a of the Manual).
• #    B-exceptional instructions -- The three B-line operations B = S', B' = B - S and S' = B are provided both with and (#) without the usual B-modification of the instruction carried out before it is decoded and obeyed.
• Dummy Instruction T£ -- This is not given in Chapter 1. It presumably did nothing when obeyed. B-modification is also suppressed for the Dummy instruction.
  

Summary Instruction Code (ordered numerically)

//		H as mag. instr.		T/		A' = S+	(Key)
/E		S' = M		TE		**
/@		standardise		T@		**
/A		S' = M, M' = 0		TA		S' = L, A' = 0
/:		S as mag. instr.		T:		A' = 0
/S		S' = L		TS		**
/I		L' = M, M' = L		TI		A' = A + S+
/U		S' = L, L' = M, M' = 0		TU		**
/½		A' = A - D S+		T½		A' = S±
/D		A' = A - D S±		TD		A' = A or S±
/R		Sideways adder		TR		A' = A and S±
/J		M' = M + S		TJ		A' = A neq S±
/N		A' = A + D S+		TN		A' = A - S±
/F		A' = A + D S±		TF		A' = -S±
/C		D' = S+		TC		A' = A + S±
/K		D' = S±		TK		A' = 2S±
/T		B-cond. direct jump		TT		B' = s
/Z		S' = H		TZ		s' = B
/L		Stop if /L switch set		TL		B' = B - s
/W		Random number generator		TW		B' = B - s
/H		A-cond. direct jump		TH		**
/Y		**		TY		**
/P		Uncond. direct jump		TP		**
/Q		Uncond. rel. jump		TQ		**
/O		B-cond. rel. jump		TO		# B' = s
/B		**		TB		# s' = B
/G		Stop if /G switch set		TG		# B' = B - s
/"		**		T"		# B' = B - s
/M		A-cond. rel. jump		TM		# (B-exceptional
/X		**		TX		#     instructions)
/V		Hoot		TV		#
/£		**		T£		# Dummy

• The numerical ordering of the instructions is counter-intuitive. The order is strictly left then right on successive lines, whereas the logical grouping of instructions is clearly in terms of half columns. The list of arithmetic instructions in the handbook shows this clearly (remembering that binary numbers are given with l.s. bit on the l.h.s.). Presumably the most significant bit of an instruction was decoded first (this division is shown by the bar in the list above), and then the least significant digit was decoded next (shown by the two columns in each half).
• **     Unused codes -- The Handbook does not define what happens if one of these unused instructions are obeyed.
• #    B-exceptional instructions -- The last block of 8 instructions above, i.e. codes with bits 0, 4 and 5 set (100011), have B-modification suppressed (see notes above). Instructions TM, TX and TV are unused codes, and T" (and TW) appear to be duplicated versions of B' = B - s.

  
  

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