4.3 Bit manipulation

2 of 2 objectives have lessons · 0 studied · 0 secure

Lessons

Shifting bits: logical, arithmetic and cyclicMove the bits in a register left or right, see what happens to the bits that fall off, and learn why arithmetic shifts keep a negative number negative. 8 min, not started
Masks: testing, setting and clearing one bitUse AND to test a bit, OR to set one and XOR to flip one, with masks written as binary, denary or hexadecimal. 8 min, not started
One byte, eight devices: monitoring and controlPack eight on/off devices into a single byte, test sensor flags with AND, and switch devices on or off with OR and an inverse mask. 8 min, not started

Syllabus objectives

2 objectives

What Cambridge says you should be able to do, in our words. Codes are the topic number plus the objective’s position.

4.3.1

Understand and carry out binary shifts.

Logical, arithmetic and cyclic shifts; left shift and right shift.

Taught in: Shifting bits: logical, arithmetic and cyclic · 6 questions

4.3.2

Understand how bit manipulation can be used to monitor or control a device.

Carry out bit manipulation operations. Test and set a bit using bit masking. The syllabus adds to the instruction set: bitwise AND, XOR and OR of the ACC with an operand (#n, Bn or &n) or with the contents of an address; LSL #n and LSR #n, which shift the bits in ACC logically n places left or right, introducing zeros at the vacated end; and labels, which name an instruction or give a symbolic address to a memory location holding data. Questions assume only one general purpose register (ACC).

Taught in: One byte, eight devices: monitoring and control, Masks: testing, setting and clearing one bit · 13 questions