UPSD3254 STMICROELECTRONICS [STMicroelectronics], UPSD3254 Datasheet - Page 27

• Manufacturer Part Number: UPSD3254
• Description: Flash Programmable System Devices with 8032 Microcontroller Core
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

External RAM. Table 10 shows a list of the Data
Transfer instructions that access external Data
Memory. Only indirect addressing can be used.
The choice is whether to use a one-byte address,
@Ri, where Ri can be either R0 or R1 of the se-
lected
address, @DTPR.
Note: In all external Data RAM accesses, the Ac-
cumulator is always either the destination or
source of the data.
Lookup Tables. Table 11 shows the two instruc-
tions that are available for reading lookup tables in
Program Memory. Since these instructions access
only Program Memory, the lookup tables can only
be read, not updated.
The mnemonic is MOVC for “move constant.” The
first MOVC instruction in Table 11 can accommo-
date a table of up to 256 entries numbered 0
through 255. The number of the desired entry is
loaded into the Accumulator, and the Data Pointer
is set up to point to the beginning of the table.
Then:
Table 10. Data Transfer Instruction that Access External Data Memory Space
Table 11. Lookup Table READ Instruction
MOVC A, @A+DPTR
Address Width
16 bits
16 bits
8 bits
8 bits
register
MOVC A,@A+DPTR
MOVC A,@A+PC
Mnemonic
bank,
MOVX A,@DPTR
MOVX @DPTR,a
MOVX A,@Ri
MOVX @Ri,A
Mnemonic
or
a
UPSD3254A, UPSD3254BV, UPSD3253B, UPSD3253BV
two-byte
copies the desired table entry into the Accumula-
tor.
The other MOVC instruction works the same way,
except the Program Counter (PC) is used as the
table base, and the table is accessed through a
subroutine. First the number of the desired en-try
is loaded into the Accumulator, and the subroutine
is called:
The subroutine “TABLE” would look like this:
The table itself immediately follows the RET (re-
turn) instruction is Program Memory. This type of
table can have up to 255 entries, numbered 1
through 255. Number 0 cannot be used, because
at the time the MOVC instruction is executed, the
PC contains the address of the RET instruction.
An entry numbered 0 would be the RET opcode it-
self.
READ program memory at (A+DPTR)
MOV A , ENTRY NUMBER
CALL TABLE
TABLE: MOVC A , @A+PC
RET
READ program memory at (A+PC)
WRITE external RAM @DPTR
READ external RAM @DPTR
WRITE external RAM @Ri
READ external RAM @Ri
Operation
Operation
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