Datasheet

 2018 Microchip Technology Inc. Data Sheet Complete DS40002060A-page 107
ATtiny4/5/9/10
15.3.6 Operation
The TPI physical layer operates synchronously on the TPICLK provided by the external programmer. The dependency
between the clock edges and data sampling or data change is shown in Figure 15-6. Data is changed at falling edges and
sampled at rising edges.
Figure 15-6. Data changing and Data sampling.
The TPI physical layer supports two modes of operation: Transmit and Receive. By default, the layer is in Receive mode,
waiting for a start bit. The mode of operation is controlled by the access layer.
15.3.7 Serial Data Reception
When the TPI physical layer is in receive mode, data reception is started as soon as a start bit has been detected. Each bit
that follows the start bit will be sampled at the rising edge of the TPICLK and shifted into the shift register until the second
stop bit has been received. When the complete frame is present in the shift register the received data will be available for
the TPI access layer.
There are three possible exceptions in the receive mode: frame error, parity error and break detection. All these exceptions
are signalized to the TPI access layer, which then enters the error state and puts the TPI physical layer into receive mode,
waiting for a BREAK character.
• Frame Error Exception. The frame error exception indicates the state of the stop bit. The frame error exception is set if
the stop bit was read as zero.
• Parity Error Exception. The parity of the data bits is calculated during the frame reception. After the frame is received
completely, the result is compared with the parity bit of the frame. If the comparison fails the parity error exception is
signalized.
• Break Detection Exception. The Break detection exception is given when a complete frame of all zeros has been
received.
15.3.8 Serial Data Transmission
When the TPI physical layer is ready to send a new frame it initiates data transmission by loading the shift register with the
data to be transmitted. When the shift register has been loaded with new data, the transmitter shifts one complete frame
out on the TPIDATA line at the transfer rate given by TPICLK.
If a collision is detected during transmission, the output driver is disabled. The TPI access layer enters the error state and
the TPI physical layer is put into receive mode, waiting for a BREAK character.
15.3.9 Collision Detection Exception
The TPI physical layer uses one bi-directional data line for both data reception and transmission. A possible drive conten-
tion may occur, if the external programmer and the TPI physical layer drive the TPIDATA line simultaneously. In order to
reduce the effect of the drive contention, a collision detection mechanism is supported. The collision detection is based on
the way the TPI physical layer drives the TPIDATA line.
TPIDATA
TPICLK
SAMPLE
SETUP