SDA5250 Datasheet, PDF (52/143 Pages) Siemens Semiconductor Group – TVTEXT 8-Bit Microcontroller

SDA 525x
Table 9
Port 4 Configuration
CB
P4 Latch
0
0
0
1
1
0
1
1
P4 Out
0
0
0
1
Comment
x
Address
P4
Addr / P4
MOVC-Handling
MOVC-instructions may operate in two different modes, that are selected by bit MM in
MEX2. On MM = 0 MOVC will access the current bank. On MM = 1 the bits MB16 – 18
will appear at A16 – A18 during MOVC.
Bank 3
Bank 2
DPTR
PC
MM=1, MB_16-17=3, CB_16-17=2
UEC04717
Figure 18
PC and DPTR on Different Banks
CALLs and Interrupts
For flexible use of CALL and interrupts the control logic holds an own 32 levels-six-bit-
stack. Whenever a LCALL or ACALL occurs, CB16 – 18 and NB16 – 18 (MEX1) is
copied to this stack and the memory extension stackpointer is incremented. Then
NB16 – 18 is copied to CB16 – 18. Leaving subroutines through RET or RETI
decrements the stack pointer and reads the old NB and CB contents from the stack. All
six bits are required for saving to prevent conflicts on interrupt events. One additional
feature simplifies the handling of interrupts: on occurrence the bits IB16 – 18 within
MEX2 are copied to CB16 – 18 and NB16 – 18 after pushing their old contents on the
stack. This way programmers can place their ISR (Interrupt Service Routine) on specific
banks. After reset MM, MB16 – 18 and IB16 – 18 are set to zero.
Semiconductor Group
52
1998-04-08