AVR TWI (I2C) problem: Operand 1 out of range - avr

Question

I´m using Atmega2560 and 24c16A EEPROM for testing an I2C code. For every state transition, controller responds by changing the status register TWSR. After start condition is transmitted, EEPROM responds and then also for Device address and write instruction (SLA+R/W), status register updates fine. But when I transmit next 8 bits, instead of ACK (Data byte sent ACK), status changes to repeated start. The code is given below. I never could find the possible solution to make it work.
.include "./m2560def.inc"
.list
.cseg
.org 0x00
jmp inicio ; PC = 0x0000 RESET
inicio:
LDI R21, HIGH(RAMEND) ;Set Up Stack
OUT SPH, R21
LDI R21, LOW(RAMEND)
OUT SPL, R21
CALL I2C_INIT ;Initialize TWI(I2C)
CALL I2C_START ;Transmit START condition
LDI R27, 0b11010000 ;SLA(0b1001100) + W(0)
CALL I2C_WRITE ;Write R27 ato the I2C bus
LDI R27, 0b11110000 ;Data to be transmitted
CALL I2C_WRITE ;Write R27 ato the I2C bus
CALL I2C_STOP ;Transmit STOP condition
HERE: RJMP HERE
;----------------------------I2C_INIT-----------------------------
I2C_INIT:
LDI R21, 0
OUT TWSR, R21 ;Set prescaler bits to 0
LDI R21, 0x47 ;R21 = 0x47
OUT TWBR, R21 ;Fclk = 50 KHz (8 MHz Xtal)
LDI R21, (1<<TWEN) ;R21 = 0x04
OUT TWCR, R21 ;HEnable TWI (I2C)
RET
;----------------------------I2C_START-----------------------------
I2C_START:
LDI R21, (1<<TWINT)|1<<(TWSTA)|(1<<TWEN)
OUT TWCR, R21 ;Transmit START condition
WAIT1:
IN R21, TWCR ;Read Control Register TWCR into R21
SBRS R21, TWINT ;Skip the next line if TWINT is 1
RJMP WAIT1 ;Jump a WAIT1 if TWINT is 1
RET
;----------------------------I2C_WRITE -----------------------------
I2C_WRITE:
OUT TWDR, R27 ;Move the byte into TWRD
LDI R21, (1<<TWINT)|(1<<TWEN)
OUT TWCR, R21 ;Configure TWCR to send TWDR
WAIT3:
IN R21, TWCR ;Read Control Register TWCR into R21
SBRS R21, TWINT ;Skip the next line if TWINT is 1
RJMP WAIT3 ;Jump a WAIT3 if TWINT is 1
RET
;----------------------------I2C_STOP------------------------------
I2C_STOP:
LDI R21, (1<<TWINT)|1<<(TWSTO)|(1<<TWEN)
OUT TWCR, R21 ;Transmit STOP condition
RET
;----------------------------I2C_READ------------------------------
I2C_READ:
LDI R21, (1<<TWINT)|(1<<TWEN)
OUT TWCR, R21
WAIT2:
IN R21, TWCR ;Read Control Register TWCR into R21
SBRS R21, TWINT ;Skip the next line if TWINT is 1
RJMP WAIT2 ;Jump a WAIT2 if TWINT is 1
IN R27, TWCR ;Read received data into R21
RET
The output is
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(41,0): error: Operand 1 out of range: 0xb9
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(43,0): error: Operand 1 out of range: 0xb8
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(45,0): error: Operand 1 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(51,0): error: Operand 1 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(53,0): error: Operand 2 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(60,0): error: Operand 1 out of range: 0xbb
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(62,0): error: Operand 1 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(64,0): error: Operand 2 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(72,0): error: Operand 1 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(78,0): error: Operand 1 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(80,0): error: Operand 2 out of range: 0xbc
D:\ATMEL_AVR\I2C_TWI\I2C_TWI.asm(83,0): error: Operand 2 out of range: 0xbc
Assembly failed, 12 errors, 0 warnings
The code lines involved in these errors are:
OUT TWSR, R21
OUT TWBR, R21
OUT TWCR, R21
OUT TWCR, R21
IN R21, TWCR
OUT TWDR, R27
OUT TWCR, R21
IN R21, TWCR
OUT TWCR, R21
OUT TWCR, R21
IN R21, TWCR
IN R27, TWCR

Answer 1

In AVR normally all I/O registers are mapped into the memory space, starting from address 0x0020
in and out instructions could be used ONLY with the first 64 of them (with 0x20...0x5F memory addresses)
sbi, cbi, sbis and sbic has further limitation and can be used only with first 32 I/O registres (with memory address 0x20...0x3F). Please refer to the AVR Instruction Set Manual
In the datasheet to ATmega2560, section 33 "Register Summary", page 401, you can see the TWI registers have addresses 0xB8 thru 0xBD, i.e. they cannot be accessed using in and out instructions. You have to use STS and LDS.
I.e. LDS R21, TWCR instead of IN R21, TWCR etc.
Also, always be careful when accessing the first 64 registers. Make sure the corresponding names are defining their I/O and not RAM addresses. I.e. PORTA should be equal to 0x02 (IO address for in / out instruction) and not 0x22 (RAM address or PORTA, which, when accessed using in or out, equals to EEARH register).