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ST7263BEx 数据表(PDF) 29 Page - STMicroelectronics |
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ST7263BEx 数据表(HTML) 29 Page - STMicroelectronics |
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29 / 186 page ![]() ST7263Bxx Central processing unit Doc ID 7516 Rev 8 29/186 Condition Code register (CC) Reset value: 111x1xxx The 8-bit Condition Code register contains the interrupt mask and four flags representative of the result of the instruction just executed. This register can also be handled by the PUSH and POP instructions. These bits can be individually tested and/or controlled by specific instructions. 76543210 111 H I N Z C Read/write Bit 4 H Half carry This bit is set by hardware when a carry occurs between 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 instruction. The H bit is useful in BCD arithmetic subroutines. Bit 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. |
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