OK, I'm about half-way through coding some comms routines for the 2014.
Unfortunately, I'm having trouble with the data reception aspect of things.
Occasionally (like, once every ten command sequences), my receive routine
desynchronizes and locks up while waiting for a start (low) pulse. The
protocol is shown in the datasheet as follows:

Write-1:
DQ ----\           /-/----------------------------\
(1)     \_________/_/           |      |          |\
        |         | |           |      |          |
DQ ----\|         | |           |/-/-/-/----------\
(0)     \_________|_|___________/_/_/_/|          |\
        |< Tstrb >| |           |      |          |
        |< Tdsu    >|< Tdh     >|      |          |
        |< Tssu                       >|< Tsh    >|

Symbol  Parameter                     Min    Typ    Max    Unit
Tstrb   Start hold, bq2014 to host    500     -      -     Microseconds
Tdsu    Data setup                     -      -     750    Microseconds
Tdh     Data hold                     750     -      -     Microseconds
Tsh     Stop hold                     700     -      -     Microseconds
Tssu    Stop setup                     -      -     2.25   Milliseconds
(more comprehensive timing diagram on page 18 of the Bq2014 datasheet from
www.ti.com)

And here's my receive code:
; Read a byte from the Bq2014
BQ2014_READ:
    MOVLW   .8                          ; 8 data bits, LSB to MSB
    MOVWF   BQLOOP
    CLRF    BQSHIFT                     ; Clear the shift buffer
    BCF     BQFLAG_TMOUT                ; Clear the timeout flag
    BQ2014_DQ_HI                        ; Make sure DQ is in input mode
    CLRF    BQTMOUTCTR                  ; Clear the timeout counter
_BQ2014_READ_LOOP:
    DECFSZ  BQTMOUTCTR,     F           ; Decrement timeout counter
    GOTO    _BQ2014_READ_NOTMOUT        ; If no timeout, keep waiting
    BSF     BQFLAG_TMOUT                ; Timeout - set flag...
RETURN  ; ... and exit

_BQ2014_READ_NOTMOUT:                   ; no timeout
; * wait for start pulse
    CALL    _BQ2014_50US_DELAY
    BTFSC   BQ2014_DQ                   ; DQ high?
    GOTO    _BQ2014_READ_LOOP           ; If so, keep waiting

    CALL    _BQ2014_1125US_DELAY        ; Sample the bit at midpoint
    BSF     STATUS,         C           ; Assume data bit is high
    BTFSS   BQ2014_DQ                   ; Check state of DQ line
    BCF     STATUS,         C           ; If low, clear carry
    RRF     BQSHIFT,        F           ; Shift data in

    CLRF    BQTMOUTCTR                  ; Clear the timeout counter
_BQ2014_READ_WAITSTOP:                  ; * wait for stop pulse
    DECFSZ  BQTMOUTCTR,     F           ; Decrement timeout counter
    GOTO    _BQ2014_READ_NOSTOPTMOUT    ; If no timeout, keep waiting
    BSF     BQFLAG_TMOUT                ; Timeout - set flag...
    RETURN                              ; ... and exit

_BQ2014_READ_NOSTOPTMOUT:
    BTFSS   BQ2014_DQ                   ; DQ high (stop)?
    GOTO    _BQ2014_READ_WAITSTOP       ; No, wait for it to go high

    DECFSZ  BQLOOP,         F           ; Decrement loopvar, skip if =0
    GOTO    _BQ2014_WRITE_LOOP          ; Keep looping
    MOVF    BQSHIFT,        W           ; Copy data byte into W and exit.
    RETURN

Can anyone see anything that I'm doing wrong or that could be done better? I
added the timeouts to try and stop the code locking up completely. In the
main loop, I've got a chunk of code that sends the command 0x01 ("read FLAG1
register"), reads a byte then turns an LED on if there was a time out and
waits 250mS before repeating the loop.
BTW, _BQ2014_50US_DELAY is a 50uS delay routine and _BQ2014_1125US_DELAY is
a 1.125mS delay routine.

Thanks.
--
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem@dsl.pipex.com              | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.dsl.pipex.com/  | 48xCD, ARCINv6c IDE, SCSI
... Law of Insurance and Taxes - Whatever goes up, stays up.

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