C8051F326 Datasheet, PDF (71/140 Pages) List of Unclassifed Manufacturers – Full Speed USB, 16 kB Flash MCU Family

C8051F326/7
9. External RAM
The C8051F326/7 devices include 1280 bytes of on-chip XRAM. This XRAM space is split into user RAM
(addresses 0x0000–0x03FF) and USB0 FIFO space. The USB0 FIFO space is only accessible through the
USB FIFO registers.
0xFFFF
Sam e 1024 bytes as from
0x0000 to 0x03FF, wrapped
on 1K-byte boundaries
USB FIFOs
256 Bytes
A cce ssed only through U S B
FIFO registers (inaccessible
using the M O V X ins truction)
0x0400
0x03FF
0x0000
XRAM
1024 Bytes
A cc essed w ith the M O V X
instruction
Figure 9.1. External Ram Memory Map
9.1. Accessing User XRAM
User XRAM can be accessed using the external move instruction (MOVX) and the data pointer (DPTR), or
using MOVX indirect addressing mode. 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 Con-
trol Register (EMI0CN as shown in Figure 9.1). Note: the MOVX instruction is also used for writes to the
Flash memory. See Section “8. Flash Memory” on page 65 for details. The MOVX instruction accesses
XRAM by default.
For any of the addressing modes, the upper 6 bits of the 16-bit external data memory address word are
"don't cares". As a result, the 1024-byte RAM is mapped modulo style over the entire 64k external data
memory address range. For example, the XRAM byte at address 0x0000 is also at address 0x0400,
0x0800, 0x0C00, 0x1000, etc.
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