IA8044/IA8344
Data Sheet
SDLC Communications Controller
March 30, 2010
4.3
Memory Organization
4.3.1 Program Memory
Program Memory includes interrupt and Reset vectors. The interrupt vectors are spaced at 8-byte
intervals, starting from 0003H for External Interrupt 0.
Table 6. Reset Vectors
Location
0003H
000BH
0013H
001BH
0023H
Service
External Interrupt 0
Timer 0 overflow
External Interrupt 1
Timer 1 overflow
SIU Interrupt
These locations may be used for program code, if the corresponding interrupts are not used
(disabled). The program memory space is 64K, from 0000H to FFFFH. The lowest 4K of
program code (0000H to 0FFFH) can be fetched from external or internal program memory. This
selection is made by strapping pin ―EA‖ (External Address) to GND or VCC. If during reset
―EA‖ is held low, all the program code is fetched from external memory. If during reset ―EA‖ is
held high, the lowest 4K of program code (0000H to 0FFFH) is fetched from internal memory
(ROM). Program memory addresses above 4K (0FFFH) will cause the program code to be
fetched from external memory regardless of the setting of ―EA.‖
4.3.2 External Data Memory
The IA8044/IA8344 Microcontroller core incorporates the Harvard architecture, with separate
code and data spaces. The code from external memory is fetched by ―psen‖ strobe, while data
is read from RAM by Bit [7] of P3 (read strobe) and written to RAM by Bit [6] of P3 (write
strobe). The External Data Memory space is active only by addressing through use of the MOVX
instruction and the 16-bit Data Pointer Register (DPTR). A smaller subset of external data
memory (8-bit addressing) may be accessed by using the MOVX instruction with register indexed
addressing.
4.3.3 Internal Data Memory
As presented in Figure 6, the Internal Data Memory address is always one byte wide. The
memory space is 192 bytes large (00H to BFH), and can be accessed by either direct or indirect
addressing. The special function registers (SFRs) occupy the upper 128 bytes. This SFR area is
available only by direct addressing. Internal memory that overlaps the SFR address space is only
accessible by indirect addressing.
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