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MC908QC8CDTE Datasheet(PDF) 35 Page - Freescale Semiconductor, Inc |
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MC908QC8CDTE Datasheet(HTML) 35 Page - Freescale Semiconductor, Inc |
35 / 274 page Random-Access Memory (RAM) MC68HC908QC16 • MC68HC908QC8 • MC68HC908QC4 Data Sheet, Rev. 3 Freescale Semiconductor 35 . 2.5 Random-Access Memory (RAM) This MCU includes static RAM. The locations in RAM below $0100 can be accessed using the more efficient direct addressing mode, and any single bit in this area can be accessed with the bit manipulation instructions (BCLR, BSET, BRCLR, and BRSET). Locating the most frequently accessed program variables in this area of RAM is preferred. The RAM retains data when the MCU is in low-power wait or stop mode. At power-on, the contents of RAM are uninitialized. RAM data is unaffected by any reset provided that the supply voltage does not drop below the minimum value for RAM retention. For compatibility with older M68HC05 MCUs, the HC08 resets the stack pointer to $00FF. In the devices that have RAM above $00FF, it is usually best to reinitialize the stack pointer to the top of the RAM so the direct page RAM can be used for frequently accessed RAM variables and bit-addressable program variables. Include the following 2-instruction sequence in your reset initialization routine (where RamLast is equated to the highest address of the RAM). LDHX #RamLast+1 ;point one past RAM TXS ;SP<-(H:X-1) Table 2-1. Vector Addresses Vector Priority Vector Address Vector Lowest Highest IF22- IF20 $FFD0- $FFD5 Unused vectors (available for user program) IF19 $FFD6,7 PWU vector IF18 $FFD8,9 TIM2 overflow vector IF17 $FFDA,B TIM2 channel 1 vector IF16 $FFDC,D TIM2 channel 0 vector IF15 $FFDE,F ADC conversion complete vector IF14 $FFE0,1 Keyboard vector IF13 $FFE2,3 SPI transmit vector IF12 $FFE4,5 SPI receive vector IF11 $FFE6,7 ESCI transmit vector IF10 $FFE8,9 ESCI receive vector IF9 $FFEA,B ESCI error vector IF8 — Not used IF7 $FFEE,F TIM1 Channel 3 vector IF6 $FFF0,1 TIM1 Channel 2 vector IF5 $FFF2,3 TIM1 overflow vector IF4 $FFF4,5 TIM1 Channel 1 vector IF3 $FFF6,7 TIM1 Channel 0 vector IF2 — Not used IF1 $FFFA,B IRQ vector — $FFFC,D SWI vector — $FFFE,F Reset vector |
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