M68HC12A4EVB hardware modifications needed for
Contents
1. with either of the narrow modes Please note however that for the board to work in normal expanded wide mode or special expanded wide mode the socket must be removed CONTACT INFORMATION USA SWEDEN IAR Systems Inc IAR Systems AB GERMANY UK IAR Systems AG TAR Systems Ltd DENMARK TAR Systems A S One Maritime Plaza San Francisco CA 94111 Tel 1 415 765 5500 Fax 1 415 765 5503 P O Box 23051 S 750 23 Uppsala Tel 46 18 1678 00 Fax 46 18 16 78 38 Email info iar se Posthalterring 5 D 855 99 Parsdorf Tel 49 89 90 06 90 80 Fax 49 89 90 06 90 81 Email info iar de 9 Spice Court Ivory Square London SW11 3UE Tel 44 171 924 3334 Fax 44 171 924 5341 Elkjervej 30 32 DK 8230 Aabyhoj Tel 45 86 25 11 11 Fax 45 86 25 11 91 Email info iar dk Email info iar com Email info iarsys co uk www iar com Copyright 2000 IAR Systems TAR and C SPY are registered trademarks of IAR Systems IAR Embedded Workbench is a trademark of IAR Systems Windows is a trademark of Microsoft Corporation All other products are registered trademarks or trademarks of their respective owners Product features availability pricing and other terms and conditions are subject to change by IAR Systems without prior notice SIAR SYSTEMS MFFERENT ARCHITECTURES ONE SOLUTION 2 www iar com2. SIAR SYSTEMS MFFERENT ARCHITECTURES ONE SOLUTION www iar com IAR Application Note 68HC 1 2 M68HC1 2A4EVB hardware modifications needed for expanded narrow modes SUMMARY This application note describes the hardware modifications needed for expanded narrow modes The modifications are simple but essential KEYWORDS 6812 A4 M68HC12A4EVB hardware patches expanded narrow mode PROBLEM The normal expanded narrow or special expanded narrow modes cannot be used on the HC12A4EVB or boards based on this design without doing one or two hardware patches to the board The modifications that need to be done to the chip select logic are simple but essential Without them the CPU can only address external memory cells located on even addresses When confronted with the problem Motorola has neither confirmed nor denied what we believe is a hardware bug in their design Figure 4 3 on page 4 13 in the M6SHC12A4EVB evaluation board user s manual shows that CPU address line AO is used in the chip select logic for the external narrow 8 bit wide RAM and ROM It is obvious from the simplified schematic that for the narrow RAM ROM devices to be selected CS must be asserted CS 0 and AO must be kept at a low logic level AO 0 This last requirement means that all external memories will be deselected whenever AO is high i e when the CPU addresses an odd address SOLUTION Fortunately the problem is easily fixed by either con
3. necting CS directly to CE and OE of the external memories while simultaneously removing the existing connection or by replacing AO at the input of the OR gate with GND Separate OR gates are used for the RAM and ROM chip select circuits If you have an HC12A4EVB and would like to use one of the narrow modes follow these steps to patch the board using the latter alternative replacing AO at the input of the OR gate with GND 1 Get a spare 14 pin DIP socket that fits between the U3 socket and the U3 IC MC74HC32AN Quad 2 input OR gate Patching the external RAM chip select circuit 2a To remove the dependency on AO cut pin 1 of the spare socket and leave just the thick uppermost part of the pin 2b To connect the former AO OR input to GND solder a wire between pin 1 the remnants of it and pin 7 of the spare socket 2c Attach some isolating material to the remaining tip of pin 1 of the spare socket Patching the external ROM chip select circuit 3a To remove the dependency on AO cut pin 13 of the spare socket and leave just the thick uppermost part of the pin 3b To connect the former A0 OR input to GND solder a wire between pin 13 the remnants of it and pin 7 of the spare socket 3c Attach some isolating material to the remaining tip of pin 13 of the spare socket 4 Insert the spare socket between the U3 socket and the U3 integrated circuit With the extra modification socket in place the board works correctly
Download Pdf Manuals
Related Search