I2C Write Time

[Suraj143]

Can somebody tell me how much time does it take to write a byte?I use I2C module.

Standard what frequency do I need to use 100Khz or 400Khz?

 

[Pommie]

It depends on what you are writing to. For example, a 24xx1025 can write a 128 byte page in 6mS (3mS to transmit + 3mS to write).

Mike.

 

[Suraj143]

Hi Mike I use 24C08 can you tell I just need to write a "Value" to the EEPROM.

Including Start--Control Address--E2 Pointer---Data---Stop.How much time will it takes.(I'm not writing a block i just writing a Byte)

I have attached the data sheet.

 

[Pommie]

Transmit time will be around 3mS as it is a 100k device. The write time will be another 10mS. So, 13mS per byte.

Mike.

 

[Suraj143]

Oh god that is too much time.I thought I2C is really speed but its too slow.But in all over the world it is using I don't know why they using if it too slow.

PIC internal EEPROM is speeder than this that takes 4mS of time per byte.

 

[Suraj143]

I get a string of characters.I need to save UART receiving character to the 24C memory at each "RCIF".With that 13mS time I'll miss many incoming characters from UART.

 

[Nigel Goodwin]

Oh god that is too much time.I thought I2C is really speed but its too slow.But in all over the world it is using I don't know why they using if it too slow.

I2C is for a specific purpose, for interconnecting IC's on a large PCB - as such it's plenty fast enough for it's intended use.

However, in this case it's not a specific I2C limitation, it's just the writing speed of EEPROM - you should use block mode to make it faster.

 

[Suraj143]

Nigel can you give me an idea on how to do this.

I get a string of characters from a PC (over 200-300 characters).I want to save these characters for later use.How can I achieve this?

I have not decided the PIC yet what ever you all suggest I can use it

 

[kamdy]

Nigel can you give me an idea on how to do this.

I get a string of characters from a PC (over 200-300 characters).I want to save these characters for later use.How can I achieve this?

I have not decided the PIC yet what ever you all suggest I can use it

The first thing you have to receive the ( 200-300 characters ) and sore them in a RAM buffer in your system then start writing them to the 24C08

 

[Nigel Goodwin]

As kamdy said.

 

[Suraj143]

Now here the problem comes.

Let say I'm receiving 300 characters & I have 200 free RAM .So I'll receive UART characters & save them in GP RAM.After receiving I start writing to 24C08 then it will take 13mS X 200 = 2600mS time,this will miss many characters in the balance 100 receiving characters.

 

[Nigel Goodwin]

Now here the problem comes.

Let say I'm receiving 300 characters & I have 200 free RAM .So I'll receive UART characters & save them in GP RAM.After receiving I start writing to 24C08 then it will take 13mS X 200 = 2600mS time,this will miss many characters in the balance 100 receiving characters.

Choose a PIC with more RAM - also use block writing mode so you can write them much faster.

For that matter, use handshaking on the link from the PC.

 

[nickelflippr]

You can also crank up the speed to 1000kbps, at the expense of lower value pullup resistors. It's been a while, but 1kΩ pullups would probably be in the ballpark.

 

[Suraj143]

Ok guys thanks for your comments.

In block write mode i'm going to write 16 bytes at once.after the stop condition do i need to wait 10ms X 16 = 160ms ?

For the time being i have a single byte write routine.in that also i wait 10ms after stop condition.

 

[Pommie]

Byte and block write take the same time.

Mike.

 

[Nigel Goodwin]

Byte and block write take the same time.

To make this a little clearer, if it takes 10ms to write one byte, then it takes the same 10ms to write a 16 byte block, so it's 16 times faster.

 

[Suraj143]

I'm writing some data to the 24C08 & it will display on LED's.
The problem is everytime from the value 13 onwards the data is incorrect.
(I guess that there is some problem with lower 4 bits of pointer address)

The data is correct when I write them from location 0x00 instead of 0x04.

;================================================================
;write the data to the 24C08
;70h-7Fh contains data
;================================================================		

Write_24C08	movlw	b'00000100'		; Write from 0x04
		movwf	E2_Add_Low
		clrf	E2_Add_High
		movlw	70h
		movwf	FSR
		movlw	.16
		movwf	Byte_Count		; write 16 bytes at once
		call	I2C_Page_Write
		---
		---


I2C_Page_Write	call	I2C_Start
		rlf	E2_Add_High,W
		andlw	b'00001110'
		iorlw	b'10100000'		; Slave Address - WR
		call	I2C_Write
		movf	E2_Add_Low,W
		call	I2C_Write
		;			
Page_Write_Loop	movf	INDF,W
		call	I2C_Write
		incf	FSR,F
		decfsz	Byte_Count,F
		goto	Page_Write_Loop
		call	I2C_Stop
		call	Delay10
		return

;==============================================
;Show the written data on the display
;==============================================

Show_Setup	movlw	.16
		movwf	Byte_Count
		movlw	b'00000100'
		movwf	E2_Add_Low
		;
Show_Loop	call	I2C_Byte_Read
		movwf	Number
		call	Display_Number		; show on LED's
		call	Delay255
		call	Delay255
		call	Delay255
		call	Delay255
		incf	E2_Add_Low,F		; increment E2 Pointer
		decfsz	Byte_Count,F
		goto	Show_Loop
		goto	Show_Setup


I2C_Byte_Read	call	I2C_Start
		movlw	b'10100000'		; Slave Address - WR
		call	I2C_Write
		movf	E2_Add_Low,W
		call	I2C_Write
		call	I2C_Restart
		movlw	b'10100001'		; Slave Address - Read
		call	I2C_Write
		call	I2C_Read
		movf	SSPBUF,W
		call	NACK_Slave
		call	I2C_Stop
		return

 

[Pommie]

A page write always starts and ends on a page boundary and so the bottom 4 bits of the address should be zero.

Mike.

 

[Suraj143]

So that means I cannot never write from 0x04 location?So always I must start with 0x00?

 

[Pommie]

You can write to location 4 but if you write 16 bytes then the last bytes will go in location 0 to 3. I.E. it wraps around in the 16 byte page.

Mike.