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2.1.2 - Long addressing mode
Long addressing mode uses one of the four DPP
registers to specify a physical 18-bit or 24-bit
address. Any word or byte data within the entire
address space can be accessed in this mode. All
devices support an override mechanism for the
DPP addressing scheme (see section 2.1.3 - DPP
override mechanism).
Long addresses (16-bit) are treated in two parts.
Bits 13...0 specify a 14-bit data page offset, and
bits 15...14 specify the Data Page Pointer (1 of 4).
The DPP is used to generate the physical 24-bit
address (see Figure 1).
All ST10 devices support an address space of up
to 16MByte, so only the lower ten bits of the
selected DPP register content are concatenated
with the 14-bit data page offset to build the physi-
cal address.
Note:
Word accesses on odd byte addresses
are not executed, but rather trigger a
hardware trap. After reset, the DPP regis-
ters are initialized so that all long
addresses are directly mapped onto the
identical physical addresses, within seg-
ment 0.
The long addressing mode is referred to by the mnemonic “mem”.
Figure 1 : Interpretation of a 16-bit long address
Table 2 : Summary of long address modes
Mnemo
Physical Address
Long Address Range
Scope of Access
mem
(DPP0)
|| mem^3FFFh
0000h...3FFFh
Any Word or Byte
(DPP1)
|| mem^3FFFh
4000h...7FFFh
(DPP2)
|| mem^3FFFh
8000h...BFFFh
(DPP3)
|| mem^3FFFh
C000h...FFFFh
mem
pag
|| mem^3FFFh
0000h...FFFFh (14-bit)
Any Word or Byte
mem
seg
|| mem
0000h...FFFFh (16-bit)
Any Word or Byte
0
15
14 13
16-bit Long Address
DPP0
DPP1
DPP2
DPP3
14-bit page offset
24-bit Physical Address
selects Data Page Pointer
0
9
0
23
13
14
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