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MC146805E2CFN Arkusz danych(PDF) 9 Page - InnovASIC, Inc |
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MC146805E2CFN Arkusz danych(HTML) 9 Page - InnovASIC, Inc |
9 / 31 page IA6805E2 Data Sheet Microprocessor Unit As of Production Version 00 Copyright © 2002 ENG21108140100 www.innovasic.com innovASIC Customer Support: The End of Obsolescence ™ Page 9 of 31 1-888-824-4184 I(Interrupt Mask Bit) The interrupt mask bit indicates that both the external interrupt and the timer interrupt are disabled (masked). If an interrupt occurs while this bit is set, the interrupt is latched and is processed as soon as the interrupt bit is cleared. H(Half Carry Bit) The half carry bit indicates that a carry occurred between bits 3 and 4 of the ALU during an ADD or ADC operation. Resets: The MPU can be reset by initial power up or by the external reset pin (reset_n). POR(Power On Reset) Power on reset occurs on initial power up. It is strictly for power initialization conditions and should not be used to detect drops in the power supply voltage. There is a 1920 t CYC time out delay from the time the oscillator is detected. If the reset_n pin is still low at the end of the delay, the MPU will remain in the reset state until the external pin goes high. Reset_n The reset_n pin is used to reset the MPU. The reset pin must stay low for a minimum of t cyc to guarantee a reset. The reset_n pin is provided with a Schmitt Trigger to improve noise immunity capability. Interrupts: The MPU can be interrupted with the external interrupt pin (irq_n), the internal timer interrupt request, or the software interrupt instruction. When any of these interrupts occur, normal processing is suspended at the end of the current instruction execution. The processor registers are saved on the stack (stacking order shown in Figure 7) and the interrupt mask (I) is set to prevent additional interrupts. Normal processing resumes after the RTI instruction causes the register contents to be recovered from the stack. When the current instruction is completed, the processor checks all pending hardware interrupts and if unmasked (I bit clear) proceeds with interrupt processing. Otherwise, the next instruction is fetched and executed. Masked interrupts are latched for later interrupt service. External interrupts hold higher priority than timer interrupts. At the end of an instruction execution, if both an external interrupt and timer interrupt are pending, the external interrupt is serviced first. The SWI gets executed with the same priority as any other instruction if the hardware interrupts are masked (I bit set). Figure 8 shows the Reset and Interrupt processing flowchart. |
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