TC1796
System Units (Vol. 1 of 2)
LMB External Bus Unit
User’s Manual 13-28 V2.0, 2007-07
EBU, V2.0
13.5.2 Chip Select Control
The EBU generates several chip select signals (see Figure 13-10):
•CSx, which is activated by accesses to the memory regions.
• CSEMU, which is activated by accesses to the emulator memory region.
• CSOVL, which is generated internally when the overlay memory region is accessed.
•CSGLB, which is generated internally when one of CSx becomes active.
•CSCOMB
, which is a combination of CSEMU, CSGLB, and CSOVL.
• Details about the chip select control logic as implemented in the TC1796 are shown
in Figure 13-10.
The four chip select lines CSx are all available at dedicated chip select outputs. The
internal CSGLB
signal is controlled by bit field EBU_CON.GLOBALCS. The bits in this
bit field make it possible to individually enable/disable each of the CSx lines for CSGLB
generation. In a similar way, CSOVL is controlled by the bits of bit field
EBU_EMUOVL.OVERLAY. Finally, CSEMU, CSGLB, and CSOVL can be individually
enabled/disabled for the combined chip select output signal CSCOMB generation.
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