Calibre UK PICA93LV User Manual
CALIBRE
Issue 1.3
Page 19
22/07/99
4.3.7.
I2C Restart and Address Sending Routine
Function definition:
restart%(slaveaddress as integer setnack as integer)
Usage:
i2cstatus% = restart(slaveaddress%, setnack%)
Function:
procedure to send Restart and slave address of device which is to be
communicated with, without a Stop having been sent at the end of the last
transmission/reception. This routine is particularly useful for reading
memories which must first have a data pointer written to them to select where
the read is to occur from, and must then have their read address sent with a
Restart to proceed with the read operation.
communicated with, without a Stop having been sent at the end of the last
transmission/reception. This routine is particularly useful for reading
memories which must first have a data pointer written to them to select where
the read is to occur from, and must then have their read address sent with a
Restart to proceed with the read operation.
Parameters are:
slaveaddress%
The slave address of the device which is to be communicated with. This will
be an even number if the communicated with. This will be an even number if
the adapter is to write to the slave, add 1 to get an odd number if the adapter
is to read from the slave.
be an even number if the communicated with. This will be an even number if
the adapter is to write to the slave, add 1 to get an odd number if the adapter
is to read from the slave.
setnack%
This controls whether the Parallel I2C Communications Adapter transmits an
Acknowledge down the I2C Bus on reception of a byte. The last byte received
during a transfer must not be acknowledged, in all other cases acknowledge
must be enabled. If setnack% = 0 then acknowledge is enabled, if setnack%
= 1 then acknowledge is disabled. Therefore, if a read (odd numbered)
address is being sent AND only 1 Byte is to be read, setnack% should be set
to = 1; in all other cases it must be clear = 0.
Acknowledge down the I2C Bus on reception of a byte. The last byte received
during a transfer must not be acknowledged, in all other cases acknowledge
must be enabled. If setnack% = 0 then acknowledge is enabled, if setnack%
= 1 then acknowledge is disabled. Therefore, if a read (odd numbered)
address is being sent AND only 1 Byte is to be read, setnack% should be set
to = 1; in all other cases it must be clear = 0.
Value Returned:
i2cstatus%
The value returned depends on whether the Start and address were sent.
If the start and address have been sent then the status returned will either be
&H00 (bus busy data sent and acknowledged), or &H08 (bus busy, data sent
but not acknowledged).
&H00 (bus busy data sent and acknowledged), or &H08 (bus busy, data sent
but not acknowledged).
If the start or the address cannot be sent (either the bus remained busy or the
address did not get sent) then the last status read IORed with &H8000 will be
returned.
address did not get sent) then the last status read IORed with &H8000 will be
returned.
The function will read the status a number of times before returning an error
condition - this number is defined by the MAXNUMBEROFGOES constant
defined in I2CINC.BAS, this value may be altered to suit your system.
condition - this number is defined by the MAXNUMBEROFGOES constant
defined in I2CINC.BAS, this value may be altered to suit your system.
I2C status on exit
&H00 bus busy and address sent and acknowledged
&H08 bus busy and address sent but not acknowledged
&H80 bus busy and address not sent.
(see Appendix A for details of Status codes).
Example Usage:
(see also sample programs)
Sub main
slaveaddress% = &HA1
' I2C Address, this is a typical slave read address
setnack% = 0
' Enable Acknowledge (see parameter descriptions)
i2cstatus% = restart(slaveaddress%, setnack%)
trash% = readbyte(setnack%) ' read the address from the adapter and discard
End Sub