How to switch register banks. As stated above, register bank 0 is the default when the is powered up. We can switch to other banks by use of the PSW program status word register. See Example Stack in the This information could be data or an address.
The CPU needs this storage area since there are only a limited number of registers. How stacks are accessed in the The register used to access the stack is called the SP stack pointer register.
The stack pointer in the is only 8 bits wide, which means that it can take values of 00 to FFH. When the is powered up, the SP register contains value This means that RAM location 08 is the first location used for the stack by the In other words, a register is pushed onto the stack to save it and popped off the stack to retrieve it.
The job of the SP is very critical when push and pop actions are performed. Pushing onto the stack. In the the stack pointer SP points to the last used location of the stack. As we push data onto the stack, the stack pointer SP is incremented by one. Notice that this is different from many microprocessors, notably x86 processors in which the SP is decremented when data is pushed onto the stack.
Examining Example , we see that as each PUSH is executed, the contents of the register are saved on the stack and SP is incremented by 1. Notice that for every byte of data saved on the stack, SP is incremented only once. Notice also that to push the registers onto the stack we must use their RAM addresses. Popping from the stack. Popping the contents of the stack back into a given register is the opposite process of pushing.
With every pop, the top byte of the stack is copied to the register specified by the instruction and the stack pointer is decremented once. Example demonstrates the POP instruction. The upper limit of the stack. In the Power Down Mode, the oscillator will be stopped and the power will be reduced to 2V.
If 1, doubles the baud rate using Timer 1. If 0, normal timer 1 baud rate. It is located as an address of 98H. It also contains bits to indicate if the Timers has overflowed.
If 1, Interrupt 1 occurs on falling edge. If 0, Interrupt 1 occurs on low level. If 1, Interrupt 0 occurs on falling edge. If 0, Interrupt 0 occurs on low level. The lower four bits are used to configure Timer0 and the higher four bits are used to configure Timer1. If a bit is SET, the corresponding interrupt is enabled and if the bit is cleared, the interrupt is disabled.
The Bit7 of the IE register i. If set to 1, Serial Port interrupt is enabled. If set to 0, Serial Port interrupt is disabled. If set to 1, Ext. Interrupt 1 is enabled. If set to 0, Ext. Interrupt 1 is disabled.
Download the pdf document of registers explanation. TCON is an 8-bit register. Its bits are used for generating interrupts internal or external. The most important bits of the timer TR and TF are also in it. TR timer run and TF timer overflow bits which we use in almost all over timer applications are in it. TCON register. These two registers TH and TL are timer high byte and timer low byte, 0 and 1 are the timers numbers. They are bit registers.
How to calculate values for TH and TL registers here is an example click on the link below. There are 4 modes in which timer can be loaded. It is bit addressable. There are five different modes four are shown above in the diagram. The most common mode is mode 1. TB8 and RB8 is used for serial modes 2 and 3. TI and RI are important bits.
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