HC12: Accesssing external RAM using CS1

NZ_Design — Wed, 13 Sep 2006 03:30:51 GMT

I are new to code warrier and are trying to setup the ability to access external RAM on the address bus.

I are using the softec HCS12x starter kit.

I have set an variable in my code

#pragma DATA_SEG __DPAGE_SEG Bat_RAM

char cExt_RAM;

#pragma DATA_SEG DEFAULT

I are setting cExt_RAM = 0x47.

And then trying to read it and send it back out the serial port (should get ‘G’ on my hyperterminal).

Works if I initialize it in internal ram.

In my startup code I have set Bat_RAM

SEGMENTS /* paged RAM */

BatteryRAM = READ_WRITE 0x200000 TO 0x20FFFF;

END

PLACEMENT

Bat_RAM INTO BatteryRAM;

END

In the map file cExt_RAM is mapped to 0x200000

This sould mean that it is mapped to CS1.

In my startup code I have set the device up as follows.

MODE = 0xA0; // MODC = 1, MODB = 0, MODA = 1 (Normal Expanded Mode)

ECLKCTL = 0x43; // NECLK = 0 (Enabled)

// NECLKX2 = 1 (Disabled)

// EDIV = 3 (Bus clock div 4)

EBICTL0 = 0x34; // ITHRS = 0 (5v Logic levels).

// HDBE = 1 (16b data bus enabled

// Enable Address lines ADDR0:19 + /UDS

EBICTL1 = 0x07; // EWAITE = 0 (External wait Enabled is disabled)

// External Access stretch set to max of 8 cycles.

// alter once working.

MMCCTL0 = 0x0F; // CS0:3 = 1 (Enabled)

MMCCTL1 = 0x05; // EROMON = 1, ROMHM = 0, ROMON = 1

CLKSEL &= 0x7F; // Ensure PLL unsellected

for (i=0; i < 800; i++);

SYNR = 39; // 40 Mhz Bus clock

for (i=0; i < 800; i++);

REFDV = 15; // 40 Mhz Bus clock

for (i=0; i < 800; i++);

while (CRGFLG & 0x08 == 0x08);

CLKSEL = 0x80;

for (i=0; i < 800; i++);

I are experanced with the standard HCS12 but new to the S12x.

As far as I can tell the CS should work.

If I scope CS1 it doesn’t change state. Also the ECLK is not being stretched for the data read/write.

Can you please point me in the right direction.

Regards,

Daniel Rogers

Message Edited by CrasyCat on 2007-04-13 02:21 PM

Re: Accesssing external RAM using CS1

CompilerGuru — Wed, 13 Sep 2006 05:58:22 GMT

Use
#pragma DATA_SEG __GPAGE_SEG Bat_RAM

DPAGE is for a HC12 A4, not for a HCS12X.

Also use the 'G suffix for the global addresses in the prm file.
E.g.:

BatteryRAM = READ_WRITE 0x200000'G TO 0x20FFFF'G;

(also use 'G only for this one, keep the logical ones for code)

Also either make BatteryRAM NO_INIT, or add a option -D__FAR_DATA to your compiler options (by default far data is not initialized).

Daniel

Re: Accesssing external RAM using CS1

NZ_Design — Wed, 13 Sep 2006 06:28:07 GMT

Thanks I are underway and working.

Daniel

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