Maxim Integrated High-Speed Microcontroller Users Guide: DS80C390 Supplement - Manual (Page 30)

High-Speed Microcontroller User’s Guide: DS80C390 Supplement
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EXTENDED STACK POINTER REGISTER (ESP)
7 6 5 4 3 2 1 0
SFR 9Bh 1 1 1 1 1 1 ESP.1 ESP.0
R-1 R-1 R-1 R-1 R-1 R-1 RW-0 RW-0
R = Unrestricted Read, W = Unrestricted Write, -n = Value after Reset
Bits 7-2 Reserved
ESP.1-0
Bits 1-0 Extended Stack Pointer. This register contains the upper 2 bits of the 10-bit
stack pointer. When the SA bit is set, any overflow of the SP from FFh to 00h
will increment the ESP by 1, and any underflow of the SP from 00h to FFh will
decrement the ESP by 1. The ESP register is ignored when SA = 0, but is still
read/write accessible. Configuring the 4K block of SRAM as program and/or data
memory (IDM1,IDM0=11b) will disable the extended stack mode. Internal logic
will take into consideration the programming conditions imposed by the SA,
IDM1 and IDM0 bits within the MCON register, to allow access to the 1K Stack
Memory. See ACON register for more detail.
ADDRESS PAGE REGISTER (AP)
7 6 5 4 3 2 1 0
SFR 9Ch
RW-0 RW-0 RW-0 RW-0 RW-0 RW-0 RW-0 RW-0
R = Unrestricted Read, W = Unrestricted Write, -n = Value after Reset
AP.7-0
Bits 7-0 Address Page Register. The AP Register (AP) supports extended program and
data addressing (>64KB) capabilities in the 22-bit paged addressing mode (AM1,
AM0 = 01b), and is fully compatible with the original 8052 16-bit addressing
mode. When executing LJMP or LCALL instructions in paged addressing mode,
the microcontroller automatically loads bits 23:16 of the program counter with
the contents of the AP register to calculate the new LCALL or LJMP address.
The AP register affects only the previous instructions, and is not incremented
during a program counter rollover from FFFFh to 0000h. This register is a
general-purpose SFR when not operating in 22-bit paged mode.
Executing interrupts while in 22-bit paged addressing mode pushes the three
bytes of the program counter onto the stack, but not the AP register itself. The AP
register should be saved at the beginning of the ISR if it will be modified inside
the ISR. Following the execution of a RETI instruction, the processor will
automatically reload the entire 24 value of the PC with the original address from
the stack, again leaving the contents of the AP register unchanged.