Memory Space And Addressing; Y-Memory Space; Figure 3-2.Data (Y) Memory Space - Lucent Technologies DSP1617 Information Manual

DSP1611/17/18/27/28/29 DIGITAL SIGNAL PROCESSOR Information Manual
Software Architecture April 1998

3.2 Memory Space and Addressing

The DSP1611/17/18/27/28/29 has two memory spaces: the X-memory space and the Y-memory space. They are
differentiated by which addressing unit they use and not by the physical memory they use. The dual-port RAM is in
the Y space and the X space, but it can be at different addresses. The Y addressing arithmetic unit (YAAU), unique
to the Y-memory space, is particularly suited for addressing memory that contains data or operands for the pro-
cessing units. The X addressing arithmetic unit (XAAU), unique to the X-memory space, is particularly suited for
program control and addressing memory that contains the instructions and coefficients as operands.
The internal dual-port RAM can be accessed in both the Y space and the X space. This RAM has multiple 1 Kword
banks, and, as long as the banks accessed are different, simultaneous data and instruction accesses can be
made. If the same bank is accessed from both memory spaces simultaneously, an extra instruction cycle (one
wait-state) is added to carry out the transfer and the Y space transfer is performed before the X space transfer.

3.2.1 Y-Memory Space

The Y-memory space is shown in Figure 3-2. Associated with the Y space are the Y addressing arithmetic unit
(YAAU), the Y address bus (YAB), the Y data bus (YDB), and the external memory interface (EMI). The 64K mem-
ory space is divided into four segments (RAM, IO, ERAMLO, and ERAMHI), as shown in Table 3-7. The selection
of a segment is automatic corresponding to the address in the YAAU. The segment for the internal RAM is further
divided into multiple 1K banks. The addresses are decoded in the YAAU, and an enable wire is provided for each
of the three external segments and for each of the internal RAM banks.
OFF-CHIP
EXTERNAL MEMORY ADDRESS BUS
YAB
YAAU
INTERNAL
EXTERNAL EXTERNAL EXTERNAL
DUAL-PORT
ERAMHI ERAMLO IO
RAM
YDB DATA BUS
EXTERNAL MEMORY DATA BUS
5-4110
Figure 3-2. Data (Y) Memory Space
DRAFT COPY
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