SDA5523 Micronas Semiconductor, SDA5523 Datasheet - Page 50

• Manufacturer Part Number: SDA5523
• Description: SDA55xx TVText Pro
• Manufacturer: Micronas Semiconductor

SDA 55xx
2.5.4. Instructions on which Memory Extension
The following instruction are used to access the
extended memory space:
– LJMP
– MOVC
– MOVX
– LCALL
– ACALL
– RET
– RETI
2.5.4.1. Program Memory Banking (LJMP)
After reset the bits for current bank (CB) and next bank
(NB) are set to zero. This insures that the microcontrol-
ler starts like a standard 8051 microcontroller at
address 00000
When a jump to another bank is required, software
changes the bits NB16 … 19 to the appropriate bank
address (before LJMP instruction).
When a LJMP is encountered in the code, the MMU
copies the NB16 … 19 (next bank) bits to CB16 … 19
(current bank). Note that the NB bits are not destroyed.
Bits related the Extended Memory address would
appear at the pins A16 … A19. These address line
have the same timing requirements compared to nor-
mal address lines A0…A15 and must be stable at the
same time.
Only with LJMP above mentioned action is performed,
other jmp instructions have no effect.
CB bits are read only.
2.5.4.2. MOVC Handling
There are two modes for MOVC instructions. The
mode is selected by MM bit in MEX2.
2.5.4.2.1. MOVC with Current Bank
When MM bit = ‘0’, MOVC will access the current
bank. The CB16 … CB19 bits would appear as
addresses A16 … A19 during MOVC instructions.
2.5.4.2.2. MOVC with Memory Bank
When MM bit = ‘1’, MOVC will access the Memory
bank. The MB16 … MB19 bits would appear as
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would act
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addresses A16 … A19 during MOVC instructions.
Note: MEX1 is not destroyed.
2.5.4.2.3. MOVX Handling
There are two modes for MOVX instructions. The
mode is selected by MXM bit in MEX3.
2.5.4.2.4. MOVX with Current Bank
When MXM bit = ‘0’, MOVX will access the current
bank. The CB16 … CB19 bits would appear as
addresses A16 … A19 during MOVX instructions.
2.5.4.2.5. MOVX with Data Memory Bank
When MXM bit = ‘1’, MOVX will access the Data mem-
ory bank. The MX16 … MX19 bits would appear as
address A16 … A19 during MOVX instructions.
Note: MEX1 is not destroyed.
2.5.4.3. CALLs and Interrupts
2.5.4.3.1. Memory Extension Stack
For Interrupts and Calls the Memory extension Stack is
required. Stack pointer MEXSP provides the stack
depth of up to 128 Bytes. Stack width is 1 Byte. In
TVTPro 128 Bytes stack is implemented.
2.5.4.4. Stack Full
No indication for stack full is provided. The user is
responsible to read MEXSP SFR to determine the sta-
tus of the MEXSP stack.
2.5.4.5. Timing
The MMU outputs the address bits A19 … A16 at the
same time as the normal addresses A15 … A0.
Stack operation signals, SAdd[6:0], SDataI[7:0],
SDataO[7:0], SRd and SWr have the same timing as
internal RAM signals.
2.5.4.6. Interfacing Extended Memory
The address bits A19, A18, A17, A16 are used to
decode extended memory.
2.5.4.7. Application Examples
MOVC
DATA SHEET
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