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ZBasic System Library
175
ZX Microcontroller Family
OpenI2CSlave
Type
Subroutine
Invocation
OpenI2CSlave(slaveAddr)
OpenI2CSlave(slaveAddr, channel)
Parameter
Method
Type
Description
slaveAddr
ByVal
Byte
The I2C slave address to which to respond.
channel
ByVal
Byte
The I2C channel to open (0-4).
Discussion
This subroutine immediately activates the I2C controller in slave mode. If the optional channel
parameter is not given, channel 0 is assumed. Note that use of channels 1-4 are supported only on
devices that have multiple I2C controllers. See the description of OpenI2C for more details about the
correspondance between channel numbers and hardware controllers.
If you activate slave mode, you must also provide an interrupt handler for the TWI vector (aka the I2C
vector). While slave mode is active, calls to CmdI2C() and the low level I2C commands are ineffective for
the I2C channel in use. Slave mode can be canceled by calling CloseI2C(), specifying the channel
number specified or implied in the call to OpenI2Cslave().
While slave mode is active, the device will respond to reads and writes on the I2C bus referring to its
slave address which is the value of the slaveAddr parameter with the least significant bit set to zero. If
the least significant bit of the slaveAddr parameter is set, the slave can respond also to “general call”
traffic on the bus.
The table below gives the pin numbers used for the SDA and SCL signals on various ZX devices.
SDA and SCL Pins
ZX Models
SDA
SCL
ZX-24n, ZX-24s
11, C.1
12, C.0
ZX-40n, ZX-40s
23, C.1
22, C.0
ZX-44n, ZX-44s
20, C.1
19, C.0
ZX-24ne, ZX-24nu
11, C.1
12, C.0
ZX-328n, ZX-328l, ZX-32n, ZX-32l
27, C.4
28, C.5
ZX-1281n
26, D.1
25, D.0
ZX-1280n
44, D.1
43, D.0
ZX-24x, ZX-24xu
12, C.0
11, C.1
ZX-32a4
10, C.0
11, C.1
ZX-128a1
15, C.0
16, C.1
ZX-128ne, ZX-1281ne
11, D.1
12, D.0
ZX-328nu
21, C4
22, C.5
Example
Call OpenI2CSlave(&H50) ' activate I2C slave mode with address &H50
Resource Usage
The I2C hardware channel in use cannot be opened by OpenI2C() while slave mode is active. On the
ZX-24n, and ZX-24s, I2C slave mode cannot be used while Com2 is open since pin 11 is shared by the
SDA signal and TxD for Com2.
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