C8051F236 Silicon Laboratories Inc, C8051F236 Datasheet - Page 90

• Manufacturer Part Number: C8051F236
• Description: IC 8051 MCU 8K FLASH 48TQFP
• Manufacturer: Silicon Laboratories Inc
• Series: C8051F2xxr

Specifications of C8051F236

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 25MHz
• Connectivity: SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, POR, WDT
• Number Of I /o: 32
• Program Memory Size: 8KB (8K x 8)
• Program Memory Type: FLASH
• Ram Size: 1.25K x 8
• Voltage - Supply (vcc/vdd): 2.7 V ~ 3.6 V
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 48-TQFP, 48-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -
• Data Converters: -

C8051F2xx
11. On-Chip XRAM (C8051F206/226/236)
The C8051F206/226/236 features 1024 Bytes of RAM mapped into the external data memory space. All
address locations may be accessed using the external move instruction (MOVX) and the data pointer
(DPTR), or using indirect MOVX addressing mode. If the MOVX instruction is used with an 8-bit operand
(such as @R1), then the high byte is the External Memory Interface Control Register (EMI0CN, shown in
SFR Definition 11.1). Addressing using 8 bits will map to one of four 256-byte pages, and these pages are
selected by setting the PGSEL bits in the EMI0CN register.
NOTE: The MOVX instruction is also used for write to the Flash memory. Please see section 10 for
details. The MOVX instruction will access 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 ("wrap around") over the entire 64k
of possible address values. For example, the XRAM byte at address 0x0000 is also at address 0x0400,
0x0800, 0x0C00, 0x1000, etc. This feature is useful when doing a linear memory fill, as the address
pointer does not have to be reset when reaching the RAM block boundary.
90
Bits7–2: Not Used -read only 000000b
Bits1–0: XRAM Page Select Bits PGSEL[1:0]
Bit7
R
-
SFR Definition 11.1. EMI0CN: External Memory Interface Control
The XRAM Page Select bits provide the high byte of the 16-bit external memory address
when using an 8-bit MOVX command, effectively selecting a 256-byte page of RAM. The
upper 6 bits are "don't cares", so the 1k address blocks are repeated modulo over the entire
data memory address space.
00:0x000 – 0x0FF
01:0x100 – 0x1FF
10:0x200 – 0x2FF
11:0x300 – 0x3FF
Bit6
R
-
Bit5
R
-
Bit4
R
-
Rev. 1.6
Bit3
R
-
Bit2
R
-
PGSEL1
R/W
Bit1
PGSEL0
R/W
Bit0
SFR Address:
Reset Value
00000000
0xAF