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ST7L19 Datasheet(PDF) 19 Page - STMicroelectronics |
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ST7L19 Datasheet(HTML) 19 Page - STMicroelectronics |
19 / 138 page ST7L15, ST7L19 19/138 CPU REGISTERS (cont’d) CONDITION CODE REGISTER (CC) Read/Write Reset Value: 111x1xxx The 8-bit Condition Code register contains the in- terrupt mask and four flags representative of the result of the instruction just executed. This register can also be handled by the PUSH and POP in- structions. These bits can be individually tested and/or con- trolled by specific instructions. Bit 4 = H Half carry This bit is set by hardware when a carry occurs be- tween bits 3 and 4 of the ALU during an ADD or ADC instruction. It is reset by hardware during the same instructions. 0: No half carry has occurred. 1: A half carry has occurred. This bit is tested using the JRH or JRNH instruc- tion. The H bit is useful in BCD arithmetic subrou- tines. Bit 3 = I Interrupt mask This bit is set by hardware when entering in inter- rupt 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 in- structions and is tested by the JRM and JRNM in- structions. 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 cur- rent interrupt routine. Bit 2 = N Negative This bit is set and cleared by hardware. It is repre- sentative 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 (that is, the most significant bit is a logic 1). This bit is accessed by the JRMI and JRPL instruc- tions. Bit 1 = Z Zero This bit is set and cleared by hardware. This bit in- dicates 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. Bit 0 = C Carry/borrow This bit is set and cleared by hardware and soft- ware. 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. 70 11 1 H I N Z C 1 |
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