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Functional Description
835
SPRUI07–March 2020
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External Interface (XINTF)
14.1 Functional Description
The XINTF is mapped into three fixed memory-mapped zones as defined in Figure 14-1.
Each of the 28x XINTF zones has a chip-select signal that is toggled when an access is made to that
particular zone. On some devices the chip-select signals for two zones may be internally ANDed together
to form a single shared chip select. In this manner, the same memory is connected to both zones or
external decode logic can be used to separate the two.
Each of the three zones can also be programmed with a specified number of wait states, strobe signal set-
up and hold timing. The number of wait states, set-up and hold timing is separately specified for a read
access and a write access. In addition, each zone can be programmed for extending wait states externally
using the XREADY signal or not. The programmable wait-state, chip-select and programmable strobe
timing enables glueless interface to external memories and peripherals.
The Set-up, Hold, and Access wait states for each XINTF zone are user-configurable using the associated
XTIMINGx registers. The access timing is based on an internal clock called XTIMCLK. XTIMCLK can be
set to the same rate as the SYSCLKOUT or to one-half of SYSCLKOUT. The rate of XTIMCLK applies to
all of the XINTF zones. XINTF bus cycles begin on the rising edge of XCLKOUT and all timings and
events are generated with respect to the rising edge of XTIMCLK.
14.1.1 Differences from the TMS320x281x XINTF
The XINTF described in this chapter is functionally very similar to the TMS320x281x XINTF. The main
differences are:
• Data Bus Width:
Each XINTF zone can be configured individually to use a 16-bit or 32-bit data bus. Using the 32-bit
mode improves performance since 32 bits of data can be read or written in a single access. The data
bus width does not change the size of the XINTF zones or memory reach. In 32-bit mode, the lowest
address line XA0 becomes a 2nd write enable. The 281x XINTF is limited to a 16-bit data bus.
• Address Bus Reach:
The address reach has been extended to 20 address lines. Zone 6 and Zone 7 both use the full
address reach of 1M x 16 words each. The 281x address reach is 512k x 16 words.
• Direct Memory Access (DMA):
All three XINTF zones are connected to the on-chip DMA module. The DMA can be used to copy code
and data to or from the XINTF while the CPU is processing other data. The 281x devices do not
include a DMA.
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