RE: 8-bit and 32-bit external memory devices with MPC555
Dobbin Allan-r11834 <[email protected]>
| Newsgroups | gmane.comp.hardware.motorola.microcontrollers |
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| Message-ID | <45E41B46B1F8D81183E4000F20D7C40B0B568536@az33exm40-bu.am.freescale.net> |
Without looking at the data sheet for this device, what you have described sounds correct. Certainly for an 8-bit port, you will use the 8 MSBs i.e. DATA[0:7] and WE[0]. Regards, Allan -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of trailrunner23 Sent: Wednesday, July 20, 2005 1:04 PM To: [email protected] Subject: [MPC500] 8-bit and 32-bit external memory devices with MPC555 Hello, We're a little confused about external memory accesses using the MPC555 and are hoping someone can set us straight. We're using a DS3832 static RAM in our design. This chip really contains two separate physical devices, a 32-bit RAM and an 8-bit RTC. The RTC has its own 8 data pins separate from the 32 RAM data pins and its own /CE, /WE, and /OE pins separate from those of the RAM. For the 32-bit RAM, MPC555 signals DATA[0:31] are connected to the RAM's 32 data pins, with MPC555 DATA[31] connected to RAM D0, MPC555 DATA[30] connected to RAM D1, etc. We are using MPC555 CS1 for chip enable of all 4 RAM bytes and WE[0:3] for write enable. For the 8-bit RAM, MPC555 signals DATA[0:7] are connected to the RTC's 8 data pins, with MPC555 DATA[7] connected to RTC D0, MPC555 DATA[6] connected to RTC D1, etc. We are using MPC555 CS2 for chip enable of the RTC and WE[0] for write enable. Can someone confirm that we're doing this correctly? It's strange that the 8 MPC555 data lines and the WE signal used for an 8-bit device are not the ones associated with the least-significant byte of the 32-bit device. Thanks for your help. Joe Pasquariello ----------------------------------------------------------- To learn more about Freescale Microcontrollers, please visit http://www.freescale.com/mcu Yahoo! Groups Links ----------------------------------------------------------- To learn more about Freescale Microcontrollers, please visit http://www.freescale.com/mcu Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/MPC500/ <*> To unsubscribe from this group, send an email to: [email protected] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/