
ST7L34, ST7L35, ST7L38, ST7L39
Central processing unit
Doc ID 11928 Rev 7
3
I
Interrupt mask
This bit is set by hardware when entering in interrupt or by software
to disable all interrupts except the TRAP software interrupt. This bit
is cleared by software.
0: Interrupts are enabled
1: Interrupts are disabled
This bit is controlled by the RIM, SIM and IRET instructions and is
tested by the JRM and JRNM instructions.
Note: Interrupts requested while I is set are latched and can be
processed when I is cleared. By default an interrupt routine is
not interruptible because the I bit is set by hardware at the start
of the routine and reset by the IRET instruction at the end of the
routine. If the I bit is cleared by software in the interrupt routine,
pending interrupts are serviced regardless of the priority level of
the current interrupt routine.
2N
Negative
This bit is set and cleared by hardware. It is representative of the
result sign of the last arithmetic, logical or data manipulation. It is a
copy of the 7th bit of the result.
0: The result of the last operation is positive or null
1: The result of the last operation is negative (in other words, the
most significant bit is a logic 1)
This bit is accessed by the JRMI and JRPL test instructions.
1Z
Zero
This bit is set and cleared by hardware. This bit indicates that the
result of the last arithmetic, logical or data manipulation is zero.
0: The result of the last operation is different from zero
1: The result of the last operation is zero
This bit is accessed by the JREQ and JRNE test instructions.
0C
Carry/borrow
This bit is set and cleared by hardware and software. It indicates an
overflow or an underflow has occurred during the last arithmetic
operation.
0: No overflow or underflow has occurred
1: An overflow or underflow has occurred
This bit is driven by the SCF and RCF instructions and tested by the
JRC and JRNC instructions. It is also affected by the ‘bit test and
branch’, shift and rotate instructions.
Table 6.
CC register description (continued)
Bit
Bit name
Function