External RAM usage of LPC22xx under KEIL FOR ARM

       To debug external RAM, I expanded a 64K RAM on CS0, which means the address starts from 0X80000000. At first, I didn't know the setting of REALVIEW, so I couldn't read or write RAM, and there was no output signal. I had to make the following settings under KEIL.

1. Under "Options for Target 'Targe 1'", select the Asm menu, fill in EXTERNAL_MODE in the input box under "Conditional Assembly Control Symbols", and then press OK to end.

2. The Startup.s file also needs some changes.

EMC_SETUP EQU 1 ; Enable external RAM control.

BCFG0_SETUP EQU 1 ; Enable CS0 control. If other chip selects are used, they must be enabled.
BCFG0_Val EQU 0x1000554A; ;

; At this time, you should pay attention to the setting of the BCFG0 register and read the content carefully. It defines the read, write, and continuous clock cycles respectively. The important thing is that if it is RAM, the RVLE bit must be set to 1, and the others should be set to a suitable value according to the speed of your RAM. Bits 29 and 28 determine the width of the RAM, 8 bits, 16 bits, 32 bits, etc.

3. Another important setting is PINSEL2

PINSEL2_Val EQU 0x0F000914

The setting is a 16-bit bus, A1-23 address lines are enabled, CS0, OE, and WE are enabled; other pins are set to I/O. Bits 4 and 5 of this register should be clear to see how many bits of bus you have selected, and then it depends on your needs.

In summary, after setting these registers, the external RAM can work normally. If the above settings are incorrect, there may be no WE signal and CS0 may not be generated; the following is a simple example.

#define RAMADDR 0x80000000 //Base address of external RAM.

void ExternRam(void)
{
    volatile unint *buf;
 unint data[512];
 unint i;
 for (i=0x00;i<512;i++)
 {
     buf=(volatile unint *) (RAMADDR | i<<1);
     * buf=i;
 }
 for (i=0x00;i<512;i++)
 {
     buf=(volatile unint *) (RAMADDR | i<<1);
     data[i]=*buf;
 }
}

If the data you write is the same as the data you read, it means that the settings are correct. When debugging, it is best to use an oscilloscope to see whether the WE, OE, CS0 and other signals are normal.