Atmel AVR User Manual

126. TST – Test for Zero or Minus
126.1. Description
Tests if a register is zero or negative. Performs a logical AND between a register and itself. The register
will remain unchanged.
Operation:
(i) Rd ← Rd • Rd
Syntax: Operands: Program Counter:
(i) TST Rd 0 ≤ d ≤ 31 PC ← PC + 1
16-bit Opcode: (see AND Rd, Rd)
0010 00dd dddd dddd
126.2. Status Register (SREG) and Boolean Formula
I T H S V N Z C
– – – ⇔ 0 ⇔ ⇔ –
S N ⊕ V, for signed tests.
V 0
Cleared.
N R7
Set if MSB of the result is set; cleared otherwise.
Z R7 • R6 • R5 • R4 • R3 • R2 • R1 • R0
Set if the result is $00; cleared otherwise.
R (Result) equals Rd.
Example:
tst r0 ; Test r0
breq zero ; Branch if r0=0
...
zero: nop ; Branch destination (do nothing)
Words 1 (2 bytes)
Cycles 1
Atmel AVR Instruction Set Manual [OTHER]
Atmel-0856L-AVR-Instruction-Set-Manual_Other-11/2016
186

Atmel AVR Specifications

General

Architecture	8-bit RISC
SRAM	Up to 16 KB
Clock Speed	Up to 20 MHz
Operating Voltage	1.8V to 5.5V
ADC	10-bit ADC
Communication Interfaces	SPI, I2C, USB
Packages	DIP, SOIC, QFN
Special Features	Watchdog Timer
Flash Memory	1KB to 256KB
EEPROM	64B to 4KB