TSC80251 TEMIC [TEMIC Semiconductors], TSC80251 Datasheet - Page 169

• Manufacturer Part Number: TSC80251
• Manufacturer: TEMIC [TEMIC Semiconductors]

5.124
TSC80251
MOVX <dest>,<src>
Function:
Move external
Description:
Transfers data between the accumulator and a byte in external data RAM. There are two types of instructions. One
provides an 8–bit indirect address to external data RAM; the second provides a 16–bit indirect address to external data
RAM.
In the first type of MOVX instruction, the contents of R0 or R1 in the current register bank provides an 8–bit address
on Port 0. 8 bits are sufficient for external I/O expansion decoding or for a relatively small RAM array. For larger arrays,
any Port pins can be used to output higher address bits. These pins would be controlled by an output instruction
preceding the MOVX.
In the second type of MOVX instruction, the data pointer generates a 16–bit address. Port 2 outputs the upper 8 address
bits (from DPH) while Port 0 outputs the lower 8 address bits (from DPL).
For both types of moves in nonpage mode, the data is multiplexed with the lower address bits on Port 0. In page mode,
the data is multiplexed with the contents of P2 on Port 2 (8–bit address) or with the upper address bits on Port 2 (16–bit
address).
It is possible in some situations to mix the two MOVX types. A large RAM array with its upper address lines driven
by P2 can be addressed via the data pointer, or with code to output upper address bits to P2 followed by a MOVX
instruction using R0 or R1.
Example :
The TSC80251 Microcontroller is operating in nonpage mode. An external 256–byte RAM using multiplexed
address/data lines (e.g., an Intel 8155 RAM/I/O/Timer) is connected to Port 0. Port 3 provides control lines for the
external RAM. Ports 1 and 2 are used for normal I/O. R0 and R1 contain 12h and 34h. Location 34h of the external
RAM contains 56h. After executing the instruction sequence:
the accumulator and external RAM location 12h contain 56h.
MOVX A,@DPTR
[Encoding]
FLAGS :
Hex Code in:
Binary Mode = [Encoding]
Source Mode = [Encoding]
1110
MOVX A,@R1
MOVX @R0,A
CY
_
0000
AC
_
OV
_
Operation:
MOVX
(A)
((DPTR))
N
_
Rev. C – May 7, 1999
Z
_