C8051F120DK Silicon Laboratories Inc, C8051F120DK Datasheet - Page 219

• Manufacturer Part Number: C8051F120DK
• Description: DEVKIT-F120/21/22/23/24/25/26/27
• Manufacturer: Silicon Laboratories Inc
• Type: MCUr

Specifications of C8051F120DK

• Contents: Evaluation Board, Power Supply, USB Cables, Adapter and Documentation
• Processor To Be Evaluated: C8051F12x and C8051F13x
• Interface Type: USB
• Silicon Manufacturer: Silicon Labs
• Core Architecture: 8051
• Silicon Core Number: C8051F120
• Silicon Family Name: C8051F12x
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: C8051F120, 121, 122, 123, 124, 125, 126, 127
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 336-1224

17. External Data Memory Interface and On-Chip XRAM
There are 8 kB of on-chip RAM mapped into the external data memory space (XRAM), as well as an Exter-
nal Data Memory Interface which can be used to access off-chip memories and memory-mapped devices
connected to the GPIO ports. The external memory space may be accessed using the external move
instruction (MOVX) and the data pointer (DPTR), or using the MOVX indirect addressing mode using R0 or
R1. If the MOVX instruction is used with an 8-bit address operand (such as @R1), then the high byte of the
16-bit address is provided by the External Memory Interface Control Register (EMI0CN, shown in SFR
Definition 17.1). Note: the MOVX instruction can also be used for writing to the Flash memory. See
tion “15. Flash Memory” on page 199
EMIF can be configured to appear on the lower GPIO Ports (P0–P3) or the upper GPIO Ports (P4–P7).
17.1. Accessing XRAM
The XRAM memory space is accessed using the MOVX instruction. The MOVX instruction has two forms,
both of which use an indirect addressing method. The first method uses the Data Pointer, DPTR, a 16-bit
register which contains the effective address of the XRAM location to be read from or written to. The sec-
ond method uses R0 or R1 in combination with the EMI0CN register to generate the effective XRAM
address. Examples of both of these methods are given below.
17.1.1. 16-Bit MOVX Example
The 16-bit form of the MOVX instruction accesses the memory location pointed to by the contents of the
DPTR register. The following series of instructions reads the value of the byte at address 0x1234 into the
accumulator A:
The above example uses the 16-bit immediate MOV instruction to set the contents of DPTR. Alternately,
the DPTR can be accessed through the SFR registers DPH, which contains the upper 8-bits of DPTR, and
DPL, which contains the lower 8-bits of DPTR.
17.1.2. 8-Bit MOVX Example
The 8-bit form of the MOVX instruction uses the contents of the EMI0CN SFR to determine the upper 8-bits
of the effective address to be accessed and the contents of R0 or R1 to determine the lower 8-bits of the
effective address to be accessed. The following series of instructions read the contents of the byte at
address 0x1234 into the accumulator A.
17.2. Configuring the External Memory Interface
Configuring the External Memory Interface consists of five steps:
MOV
MOVX
MOV
MOV
MOVX
1. Select EMIF on Low Ports (P3, P2, P1, and P0) or High Ports (P7, P6, P5, and P4).
2. Configure the Output Modes of the port pins as either push-pull or open-drain (push-pull is
3. Configure Port latches to “park” the EMIF pins in a dormant state (usually by setting them to
4. Select Multiplexed mode or Non-multiplexed mode.
most common).
logic ‘1’).
DPTR, #1234h
A, @DPTR
EMI0CN, #12h
R0, #34h
a, @R0
for details. The MOVX instruction accesses XRAM by default. The
; load DPTR with 16-bit address to read (0x1234)
; load contents of 0x1234 into accumulator A
; load high byte of address into EMI0CN
; load low byte of address into R0 (or R1)
; load contents of 0x1234 into accumulator A
Rev. 1.4
C8051F120/1/2/3/4/5/6/7
C8051F130/1/2/3
Sec-
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