📄 usi_i2cslave.s43
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;******************************************************************************
; MSP430F20xx - I2C Slave Transmitter and Receiver
;
; Description: This code library configures the MSP430 as an I2C slave device
; capable of transmitting and receiving bytes.
;
; ***THIS IS THE SLAVE CODE***
;
; Slave
; MSP430F20x2/3
; -----------------
; | XIN|-
; | |
; | XOUT|-
; | |
; | |
; | |
; | SDA/P1.7|------->
; | SCL/P1.6|------->
;
; Note: Internal pull-ups are used for SDA & SCL
;
; P. Thanigai
; Texas Instruments Inc.
; March 2008
; Built with IAR Embedded Workbench Version: 4.09A
;******************************************************************************
#include <msp430x20x2.h>
; Note: The USE_C_CONTEXT_SAVE macro is used when C functions are called from
; the library. The macro preserves registers R13 - R15 which may be corrupted
; during a C function call. If the called function is in assembler the
; macro need not be used.
# define USE_C_CONTEXT_SAVE
MODULE TI_USI_I2C_SLAVE
RTMODEL "__rt_version", "3" ; Ensure correct runtime model
;Functions
PUBLIC TI_USI_I2C_SlaveInit
RSEG DATA16_N
TI_SlavAdd DS 1
TI_LPMbit DS 1
EVEN
TI_I2CState DS 2
TI_RxFuncPtr DS 2
TI_TxFuncPtr DS 2
TI_StartFuncPtr DS 2
RSEG CODE ; Code is relocatable
EVEN
;==============================================================================
; USI module
;==============================================================================
; void TI_USI_I2C_SlaveInit(unsigned char OwnAddress, int(*StartCallback)
; (unsigned char),int(* RxCallback)(unsigned char), int(* TxCallback)
; (unsigned char))
;
; Function implements block read master reciever functionality
;
; IN: R12 Own Address
; R13 Start Callback fn. pointer
; R14 Receiver Callback fn. pointer
; R15 Transmitter Callback fn. pointer
;------------------------------------------------------------------------------
TI_USI_I2C_SlaveInit
bis.b #0xC0,&P1OUT
bis.b #0xC0,&P1REN ; Internal Pullups enable
SetupUSI mov.b #USIPE6+USIPE7+USISWRST,&USICTL0; Port, I2C slave
mov.b #USIIE+USII2C+USISTTIE,&USICTL1 ; Enable I2C mode,USI Ints
mov.b #USICKPL,&USICKCTL ; Setup clock polarity
mov.b #USIIFGCC,&USICNT ; Disable auto clear ctrl
bic.b #USISWRST,&USICTL0 ; Release USI for operation
bic.b #USIIFG,&USICTL1 ; Clear flag
clr.w &TI_I2CState ; Initialize State machine
mov.b R12,&TI_SlavAdd ; Initialize slave address
mov.w R13,&TI_StartFuncPtr ; Initialize StartCallback Ptr
mov.w R14,&TI_RxFuncPtr ; Intialize RxCallback Ptr
mov.w R15,&TI_TxFuncPtr ; Intialize TxCallback Ptr
ret
;------------------------------------------------------------------------------
USI_ISR
; Program Flow :
; Rx bytes from master: State 2->4->6->8
; Tx bytes to Master: State 2->4->10->12->14
;
;------------------------------------------------------------------------------
bit.b #USISTTIFG,&USICTL1 ; start condition received?
jnc Check_State ; if not start, check state machine
push.w R12 ; save register if used in callback
#ifdef USE_C_CONTEXT_SAVE
push.w R13
push.w R14
push.w R15
#endif
call &TI_StartFuncPtr ; Invoke StartCallback()
#ifdef USE_C_CONTEXT_SAVE
pop.w R15
pop.w R14
pop.w R13
#endif
pop.w R12 ; restore register
mov.w #2,&TI_I2CState ; Move to next state, rx address
Check_State add.w &TI_I2CState,PC ; I2C State Machine
jmp STATE0
jmp STATE2
jmp STATE4
jmp STATE6
jmp STATE8
jmp STATE10
jmp STATE12
jmp STATE14
jmp STATE16
STATE0 nop ; Idle, should not get here
bic.b #USIIFG,&USICTL1
reti
STATE2 ; Rx Slave address
push.w R12 ; Save contents of register
mov.b &USICNT,R12
and.b #0xE0,R12
add.b #0x8,R12
mov.b R12,&USICNT ; Bit counter = 8
bic.b #USISTTIFG,&USICTL1 ; Clear Start flag
mov.w #4,&TI_I2CState ; Goto next state, transmit (N)ack
bic.b #USIIFG,&USICTL1
pop.w R12 ; Restore register
reti
STATE4 ; (N)Ack Slave address
push.w R12 ; save register on stack
mov.b &USISRL,R12
rra.b &USISRL ; isolate slave address from R/w bit
and.b #0x7F,&USISRL ; isolate 7 bit slave address
cmp.b &TI_SlavAdd,&USISRL ; If SA is correct, chk tx/rx
jnz Add_NACK ; If incorrect, send NACK
bit.b #0x01,R12 ; R/w = 0 , go to receive
pop.w R12 ; restore register
jc Transmit ; R/w = 1, jump to transmit
Receive
bis.b #USIOE,&USICTL0 ; SDA = output
clr.b &USISRL ; acknowledge slave address
mov.w #6,&TI_I2CState ; next state, rx a byte
STATE4_Exit
bis.b #1,&USICNT ; Bit counter = 1
bic.b #USIIFG,&USICTL1
reti
Transmit
bis.b #USIOE,&USICTL0 ; SDA = output
clr.b &USISRL ; acknowledge slave address
mov.w #10,&TI_I2CState ; next state, tx a byte
jmp STATE4_Exit
Add_NACK ; Device address incorrect
mov.b #0xFF,&USISRL ; Send NACK
mov.w #16,&TI_I2CState ; goto next state, prep re-start
jmp STATE4_Exit
STATE6 ; Receive one byte
bic.b #USIOE,&USICTL0 ; SDA =input
bis.b #8,&USICNT ; Bit counter = 8
mov.w #8,&TI_I2CState ; goto next state, tx (N)ack
bic.b #USIIFG,&USICTL1
reti
STATE8 ; Check Data and Tx Ack ; move received data to appln. level
push.w R12
#ifdef USE_C_CONTEXT_SAVE
push.w R13
push.w R14
push.w R15
#endif
mov.b &USISRL,R12
bis.b #USIOE,&USICTL0 ; SDA = output
clr.b &USISRL ; Send ack
bis.b #1,&USICNT ; Bit counter =1
mov.w #6,&TI_I2CState
call &TI_RxFuncPtr ; Call RxCallback function
cmp.w #1,R12 ; Wake up from LPM?
#ifdef USE_C_CONTEXT_SAVE
pop.w R15
pop.w R14
pop.w R13
#endif
pop.w R12
jnz exitISR ; stay in lpm
bic.w #LPM4,0(SP) ; Wake up on exit
exitISR bic.b #USIIFG,&USICTL1
reti
STATE10 ; Transmit one byte of data
bis.b #USIOE,&USICTL0 ; SDA =output, get ready to tranmsit
push.w R12 ; save register
#ifdef USE_C_CONTEXT_SAVE
push.w R13
push.w R14
push.w R15
#endif
decd.w SP ; create variable space to store
mov.w SP,R12 ; ... tx data
call &TI_TxFuncPtr ; Call TxCallback
mov.b R12,&TI_LPMbit ; Store LPM bit
pop.b &USISRL ; move tx byte from stack to SRL
#ifdef USE_C_CONTEXT_SAVE
pop.w R15
pop.w R14
pop.w R13
#endif
pop.w R12 ; restore register
bis.b #8,&USICNT ; Bit counter = 8, send the data
mov.w #12,&TI_I2CState ; goto next state, rx (N)ack
bic.b #USIIFG,&USICTL1
reti
STATE12 ; get (N)ACK from Master
cmp.w #1,&TI_LPMbit ; Chk LPM bit
jnz Get_Ack ; Stay in LPM
bic.w #LPM4,0(SP) ; Wake up on exit
Get_Ack bic.b #USIOE,&USICTL0 ; SDA = input
bis.b #1,&USICNT ; Bit counter =1
mov.w #14,&TI_I2CState ; next state, test (N)ack
bic.b #USIIFG,&USICTL1
reti
STATE14 ; Test the (N)Ack
bit.b #0x01,&USISRL
jnc Next_Transfer ; Ack rxed ready for next transfer
bic.b #USIOE,&USICTL0 ; Nack rxed, last transmit
clr.w &TI_I2CState ; Re-initialize state machine
bic.b #USIIFG,&USICTL1
reti
Next_Transfer
mov.w #10,&TI_I2CState
jmp STATE10
STATE16 ; Reset I2C state machine on address NACK
bic.b #USIOE,&USICTL0 ; Prep for Start condition
clr.w &TI_I2CState ; Reset state machine
bic.b #USIIFG,&USICTL1
reti
;------------------------------------------------------------------------------
; Interrupt vectors
;------------------------------------------------------------------------------
COMMON INTVEC
ORG USI_VECTOR ; USI module
DW USI_ISR ;
END
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