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assaad
Joined: 09 Dec 2009
Posts: 37
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| External parallel ram problem |
 Posted: Tue Aug 24, 2010 4:01 am |
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Hi all
It was long time for me, but finally I am back with new project full of mistakes  and need your help friends.
I am using 128k external parallel ram (AS6C1008) with 18f8722. The problem that I have problem with reading and writing to the ram, it works sometimes and does not alot. I think I have mistake in hardware maybe ! or a software bug because I am new to CCS .
The routines that I use for RAM :
| Code: |
////////////////////////////////////////////////////////
byte ram_read_high(int16 address )
{
int8 value;
byte data ;
output_h(0xd0); // 0110 ce , ce2 , we, oe disable ram
output_high(pin_g0); // A16=0 ///
output_high(pin_j2);
output_low(pin_g3); // enable latch to ram ///oelram of 74hc573
value = make8(address,0); // low byte
trise=0;
trisd=0;
late=value;
//output_e(value);
value = make8(address,1); // high byte
latd=value;
//output_d(value);
output_h(0x60); // 0110 ce , ce2 , we, oe enable ram
output_high(pin_g3); // disable latch to ram ///oelram of 74hc573
trise=0xff;
data=porte;
//data=input_e();
output_h(0xd0); // 0110 ce , ce2 , we, oe disable ram
output_low(pin_g0); // A16=0 ///
output_low(pin_j2);
return (data);
}
void ram_write_high(int16 address , byte data)
{
int8 value , test,counter;
counter=0;
start_write:
output_h(0xd0); // 0110 ce , ce2 , we, oe disable ram
output_high(pin_g0); // A16=0 ///
output_high(pin_j2);
value = make8(address,0); // low byte
trise=0;
trisd=0;
late=value;
//output_e(value);
value = make8(address,1); // high byte
latd=value;
//output_d(value);
output_low(pin_g3); // enable latch to ram ///oelram of 74hc573
//#asm
//nop
//#endasm
output_h(0x10); // 0100 ce , ce2 , we, oe enable ram
//#asm
//nop
//#endasm
output_h(0x20); // 0100 ce , ce2 , we, oe enable ram
output_high(pin_g3); // disable latch to ram ///oelram of 74hc573
late=data;
//output_e(data);
output_h(0xd0); // 0110 ce , ce2 , we, oe disable ram
output_low(pin_g0); // A16=0 ///
output_low(pin_j2);
}
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I would like to upload the schematic but I could not find an option to do that.
I wish someone guide me to solve the ram issue and thanks in advanced. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Tue Aug 24, 2010 11:33 am |
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| Quote: | | I am using 128k external parallel ram (AS6C1008) with 18f8722. |
The 18F8722 has built-in hardware support for an external parallel ram.
You should study how to do it that way.
From the 18F8722 data sheet:
| Quote: |
7.0 EXTERNAL MEMORY BUS
The External Memory Bus (EMB) allows the device to
access external memory devices (such as Flash,
EPROM, SRAM, etc.) as program or data memory. It
supports both 8-bit and 16-bit Data Width modes and
four address widths from 8 to 20 bits.
Note: The External Memory Bus is not imple-mented
on PIC18F6527/6622/6627/6722
(64-pin) devices.
7.2.1 21-BIT ADDRESSING
As an extension of 20-bit address width operation, the
External Memory Bus can also fully address a 2 Mbyte
memory space. |
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assaad
Joined: 09 Dec 2009
Posts: 37
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| Posted: Thu Aug 26, 2010 8:53 am |
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Thank you.
It is ok now, there was problem in the address.
I could not use the hardware one because I am using the ports for other issue. Software one save pin for me. However its ok now. |
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