參數(shù)資料
型號: TMS320C209-57
元件分類: 數(shù)字信號處理
英文描述: Digital Signal Processor
中文描述: 數(shù)字信號處理器
文件頁數(shù): 66/132頁
文件大?。?/td> 1707K
代理商: TMS320C209-57
SPRS145G
JULY 2000
REVISED FEBRUARY 2002
66
POST OFFICE BOX 1443
HOUSTON, TEXAS 77251
1443
external memory interface (LF2407A)
The TMS320LF2407A can address up to 64K
×
16 words of memory (or registers) in each of the program, data,
and I/O spaces. On-chip memory, when enabled, occupies some of this off-chip range.
The CPU of the TMS320LF2407A schedules a program fetch, data read, and data write on the same machine
cycle. This is because from on-chip memory, the CPU can execute all three of these operations in the same
cycle. However, the external interface multiplexes the internal buses to one address bus and one data bus. The
external interface sequences these operations to complete first the data write, then the data read, and finally
the program read.
The LF2407A supports a wide range of system interfacing requirements. Program, data, and I/O address
spaces provide interface to memory and I/O, thereby maximizing system throughput. The full 16-bit address
and data buses, along with the PS, DS, and IS space-select signals, allow addressing of 64K 16-bit words in
program, data, and I/O space. Since on-chip peripheral registers occupy positions of data-memory space
(7000
7FFF), the externally addressable data-memory space is 32K 16-bit words (8000
FFFF). Note that the
global memory space of the C2xx core is not used for 240xA DSP devices. Therefore, the global memory
allocation register (GREG) is reserved for all these devices.
Input/output (I/O) design is simplified by having I/O space treated the same way as memory. I/O devices are
accessed in the I/O address space using the processor
s external address and data buses in the same manner
as memory-mapped devices.
The LF2407A external parallel interface provides various control signals to facilitate interfacing to the device.
The R/W output signal is provided to indicate whether the current cycle is a read or a write. The STRB output
signal provides a timing reference for all external cycles. For convenience, the device also provides the RD and
the WE output signals, which indicate a read cycle and a write cycle, respectively, along with timing information
for those cycles. The availability of these signals minimizes external gating necessary for interfacing external
devices to the LF2407A.
The 2407A provides RD and W/R signals to help the zero-wait-state external memory interface. At higher
CLKOUT speeds, RD may not meet the slow memory device
s timing. In such instances, the W/R signal could
be used as an alternative signal with some tradeoffs. See the timings for details.
The TMS320LF2407A supports zero-wait-state reads on the external interface. However, to avoid bus conflicts,
writes take two cycles. This allows the TMS320LF2407A to buffer the transition of the data bus from input to
output (or from output to input) by a half cycle. In most systems, the TMS320LF2407A ratio of reads to writes
is significantly large to minimize the overhead of the extra cycle on writes.
wait-state generation (LF2407A only)
Wait-state generation is incorporated in the LF2407A without any external hardware for interfacing the LF2407A
with slower off-chip memory and I/O devices. Adding wait states lengthens the time the CPU waits for external
memory or an external I/O port to respond when the CPU reads from or writes to that external memory or I/O
port. Specifically, the CPU waits one extra cycle (one CLKOUT cycle) for every wait state. The wait states
operate on CLKOUT cycle boundaries.
To avoid bus conflicts, writes from the LF2407A always take at least two CLKOUT cycles. The LF2407A offers
two options for generating wait states:
READY Signal. With the READY signal, you can externally generate any number of wait states. The READY
pin has no effect on accesses to
internal
memory.
On-Chip Wait-State Generator. With this generator, you can generate zero to seven wait states.
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