Hi,

Jinx wrote:
>Tony, why do some of your instructions include the ,A ?

well I noticed you already got an reply, but to recap,=20
it's an special ram bank than can always be accessed on the=20
18xxx chip without needing to set the ram bank selection bits.
Sort of similar to the 16F8xx series 'mirrored ram'. Quite
handy for isr routines or to pass variables between routines.
Supposedly one should be able to omitt the ',A' when using reloctable
code and the linker, but that just didn't work in the early versions.=20
This snippet was form that 'era' :)

Anyway some minor points to the state handler:

Only allows one tx/rx at a time, i.e. no i2c 'stack'.

- before statring the i2c write, the following should be
  performed:
  - check that state=3D0 and that there are no activity on the bus
  - setup i2c slave adress (if not done before)
  - fill i2c buffer with relevant data, count=3Dno.of.bytes
- call isr state handler *outside* the isr when everything is setup
  it will initiate the start condition and set state=3D1,
  form hereon everything will be handled inside the isr.


- before statring the i2c read, the following should be
  performed:
  - check that state=3D0 and that there are no activity on the bus
  - setup i2c slave adress (if not done before)
  - setup dest adress pointers (where the data will be stored)
  - setup number of bytes to read
- setup state=3D4 and call isr state handler *outside* the isr=20
  when everything is setup it will initiate the start condition and set
state=3D5,
  form hereon everything will be handled inside the isr.


Some example snippets:

*example isr handler*
INT_TEST_I2C_IRQ
=09
        ; TEST FOR COMPLETION OF VALID I2C EVENT=20
        BTFSS   PIE1,SSPIE,A    ; test if interrupt is enabled
        GOTO    INT_TEST_ANOTHER_FLAG
        BTFSS   PIR1,SSPIF,A    ; test for SSP H/W flag
        GOTO    INT_TEST_ANOTHER_FLAG ; optionally test for bus
collision (if multi master)
        BCF     PIR1,SSPIF,A    ; clear SSP H/W flag
        TSTFSZ  i2c_State,A     ; if non zero then continue i2c seq.
        CALL   I2C_INT_HANDLER  ; service valid I2C event       =09



*wait for idle* ( potential dangerous code, can loop forever, I also
use an timer to detect timeout conditions so this is circumvented )

;+++++
;       I2C_WAIT_IDLE Holds execution until there is no activity on the
i2c bus
;       Either local or remote

I2C_WAIT_IDLE
        GLOBAL  I2C_WAIT_IDLE
        ; check that there are no local activity ( all rx/tx's are done
)
I2C_WAIT_IDLE_BUSY
        TSTFSZ  i2c_State,A
        GOTO    I2C_WAIT_IDLE_BUSY

I2C_WAIT_IDLE_FLUSH
        ; test for i2c bus idle state
        BTFSC   SSPSTAT,R_W,A     ; test if transmit is progress=20
        GOTO    I2C_WAIT_IDLE_FLUSH ; module busy so wait
I2C_WAIT_IDLE_BUS
        MOVF    SSPCON2,W,A       ; get copy of SSPCON2 for status bits
        ANDLW   0x1F            ; mask out non-status bits
        BTFSS   STATUS,Z        ; test for zero state, if Z set, bus is
idle
        GOTO    I2C_WAIT_IDLE_BUS ; bus is busy so test again

        RETURN

*start write* (can be outside isr)
;+++++
;       I2C_START_TX Starts an transmission with data in i2c buffer
;       and current adress
I2C_START_TX
        GLOBAL  I2C_START_TX
        CLRF    i2c_eventflags,A
        CALL    I2C_INT_HANDLER
        RETURN

*start read* (can be outside isr)
#define I2C_RXSTART_STATE       0x04 ; i2c state for starting an rx
sequence

;+++++
;       I2C_START_RX Starts an transmission with number of byte in w
;       and current adress, data will be stored in i2c_buffer
I2C_START_RX
        GLOBAL  I2C_START_RX
        MOVWF   i2c_read_count,A; save byte counter
        CLRF    i2c_eventflags,A
        MOVLW   I2C_RXSTART_STATE       ; setup i2c state variable
        MOVWF   i2c_State,A
        CALL    I2C_INT_HANDLER ; and issue the start condition
        RETURN

/Tony

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