 'C3x DSK Daugthercard with external EPROMAn external boot EPROM or EEPROM can be added to the DSK by using the /UBOOT enable pin to enable a device in the range of 0x000000 to 0x100000 which corresponds to a bootload select using INT0. The TMS320C31 bootloader is actually DSP code that is contained in a pre-programmed ROM internal to the chip. The internal bootloader code space is mapped to 0x0000-0xFFFF and is enabled by MCBL/MP=1, which is the default for the DSK. The internal bootloader is used for normal DSK operation as well as EPROM Bootloading so there is no need to change the value of MCBL/MP. When an INT0 bootload is selected, the internal bootloader code causes the DSP to read the first external byte value (the code you want to bootload) from address 0x1000. Other interrupts select different address ranges. For example, INT2 which the DSK used for host communications is also used to bootload the DSK kernel from the host interface. If your EPROM decodes an address range less than 0x1000, you can use memory aliasing to access your bootcode at ROM_address=0x0000. You can do this with a larger EPROM by tying the upper EPROM address lines low, but this wastes EPROM space. Memory aliasing works because the external ROM is enabled over many pages, one of which is at 0x1000. If your EPROM decode range is greater than 0x1000, you will need to copy/load your bootcode at an offset of 0x1000 in the EPROM. The lower 0x1000 of space can still be accessed using an aliased memory page. The number of software wait states defined in the bus control register must be sufficient for the speed of the EPROM that you use plus the delay time for the /UBOOT signal to decode. For example, if you use an 85 nS EPROM, and the decoder takes 25 nS, plus DSP signal delay of 13 nS, You will need 123 nS of bus cycle time. With three wait states the bus read time is (3+1)*40 nS = 160 nS which ensures proper operation. In practice, if the devices are operated at or near room temperature, which widens the timing margins substantially, fewer cycles may work, but it is not suggested. The DSK host interface also requires at least one wait state to operate properly. Do not lower the wait states below this value if you plan to also use the DSK debugger. Since DSK bootloaded code primarily runs in the on-chip memory, any value of wait states will work without degrading performance. The DSK3D debugger can be used even if an external EPROM is used. The only constraint is that the first bootloader select interrupt after reset is applied will determine which bootsource will be used If the printer port is not connected, or if the DSK debugger (or other application) is not executing a command, the INT2 line will be inactive high. By then pulsing /RESET low, followed by INT0 low, the TMS320C31 will execute a bootload operation from address 0x1000.
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