DS89C420-ENG Maxim Integrated Products, DS89C420-ENG Datasheet - Page 20

• Manufacturer Part Number: DS89C420-ENG
• Description: IC MCU ULTRA 25MHZ HP 44-TQFP
• Manufacturer: Maxim Integrated Products
• Series: 89Cr

Specifications of DS89C420-ENG

• Core Processor: 8051
• Core Size: 8-Bit
• Speed: 25MHz
• Connectivity: EBI/EMI, SIO, UART/USART
• Peripherals: Power-Fail Reset, WDT
• Number Of I /o: 32
• Program Memory Size: 16KB (16K x 8)
• Program Memory Type: FLASH
• Ram Size: 1K x 8
• Voltage - Supply (vcc/vdd): 4.5 V ~ 5.5 V
• Oscillator Type: External
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 44-TQFP, 44-VQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Eeprom Size: -
• Data Converters: -

Figure 6. Memory Map
The reset default condition is a maximum on-chip program-memory address of 16kB. When accessing external
program memory, the first 16kB would be inaccessible. To select a smaller effective program memory size,
software must alter bits RMS2–RMS0. Altering these bits requires a timed access procedure as explained later.
Care should be taken so that changing the ROMSIZE register does not corrupt program execution. For example,
assume that a DS89C420 is executing instructions from internal program memory near the 12kB boundary
(~3000h) and that the ROMSIZE register is currently configured for a 16kB internal program space. If software
reconfigures the ROMSIZE register to 4kB (0000h–0FFFh) in the current state, the device immediately jumps to
external program execution because program code from 4kB to 16kB (1000h–3FFFh) is no longer located on-chip.
This could result in code misalignment and execution of an invalid instruction. The recommended method is to
modify the ROMSIZE register from a location in memory that is internal (or external) both before and after the
operation. In the above example, the instruction that modifies the ROMSIZE register should be located below the
FF
80
7F
2F
20
1F
00
Bit Addressable
128 Bytes
Indirect
Addressing
Bank 3
Bank 2
Bank 1
Bank 0
128 Bytes SFR
REGISTERS
INTERNAL
03FF
0000
3FFF
2000
1FFF
0000
INTERNAL
MEMORY
(Program)
addr from
prog mem
Memory
(Program)
400 - 7FF
8K x 8
Data OR
Memory
8K x 8
SRAM
Flash
1K x 8
Flash
20 of 47
FFFF
4000
0000
External
Program
Memory
FFFF
03FF
0000
External
Data
Memory