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5.10.3 SPI Special mode function (IOW24 only)

IO-Warrior24 has a hardware SPI interface

enabling it to talk to many peripheral devices.

IOW24 supports SPI master mode.

To enable the SPI function a report with ID 8 is

sent to interface1:

enable = $00 disables the SPI and $01 enables it.

"mode" contains flags specifying the operating

mode for the SPI:

7 - unused, write zero

6 - unused, write zero

5 - unused, write zero

4 - unused, write zero

3 - CPOL

2 - CPHA

1 - data rate MSB

0 - data rate LSB

The data rate select bits set the clock speed at

which IO-Warrior is driving SCK:

00 - 2MBit/sec

01 - 1MBit/sec

10 - 0.5MBit/sec

11 - 0.0625MBit/sec

CPHA works together with CPOL to specify which

clock edges are used to drive and sample data bits.

CPOL = 0 causes SCK to idle low between data

bytes, CPOL = 1 makes SCK idle high.

CPHA = 0 causes data to be driven on the first

clock edge and sampled on the second edge. CPHA

= 1 causes data to be driven on the second edge

(first bit gets driven before the first edge) and

sampled on the first edge.

Enabling SPI takes P0.3..P0.7 out of the control of

interface zero.

SPI does always shift data in and out

simultaneously. So there is only one command to

send data out of SPI that does also result in the

same number of bytes being read in and returned to

the host. if the intention is to only read data from

an external device it is still necessary to shift out

the same number of dummy bytes to that device.

IOW24 does not allow to use SPI and LCD at the

same time. If LCD is enabled at the time a

command to enable SPI is received the command

is ignored. This means none of the SPI commands

will be executed when received nor will they send

any response. IOW24 will acknowledge that it

received the report with the command but not

execute the corresponding function and not send

any reports in reaction to the command.

Data transfers on the SPI are initiated by a report

with ID 9:

"flags" contains the following bits:

7 - useDRDY, 1 = do handshake

6 - SSactive, 1 = /SS stays active

5 - ignoreDRDY, 1 = first byte ignores /DRDY

4 - unused, zero

3 - unused, zero

2 - data count MSB

1 - data count

0 - data count LSB

"useDRDY" allows to enable a handshaking signal

that allows the slave to signal if and when it is

ready to accept or send data.

If "useDRDY" is = 1 IO-Warrior will check for the

/DRDY signal to be low before it starts shifting a

data byte. If the slave wants to pause the data

transmission it has to pull /DRDY high before the

end of the current byte transfer.

Upon starting a data transfer it may be desired to

send the first byte without the slave signalling /

DRDY low. By setting "ignoreDRDY" to 1 the

first byte of this report is sent to the slave without

checking /DRDY. Prior to shifitng the next byte

IO-Warrior will check the status of /DRDY.

"data count" has the number of bytes to shift, only

values 1-6 are valid, others will be ignored.

IO-Warrior assertes /SS before starting to shift the

first data byte of this report and will deassert it

after completing the last byte, unless bit 6

"SSactive" is = 1. If "SSactive" is set /SS will stay

asserted after the last byte of the report has been

transfered, allowing more than 6 bytes to take part

of a single transfer.

Data shifted in by IO-Warrior during a transaction

is returned in a report with ID 9:

"count" holds the number of valid bytes in the

report.

ReportID

$08 out

enable mode

$00 $00

$00

ReportID

$09 out

flags data

data data

data

ReportID

$09 in

count data

data data

data

V 1.1.0, December 2nd 2013, for chip revision V1.0.3.0 and up