
PRODUCT SPECIFICATION
TMC22x5y
67
P
Serial Control Port (R-Bus)
In addition to the 12-wire parallel port, a 2-wire serial 
control interface is provided, and active when SER is LOW. 
Either port alone can control the entire chip. Up to eight 
TMC22x5y devices may be connected to the 2-wire serial 
interface with each device having a unique address. 
The 2-wire interface comprises a clock (SCL) and a bi-direc-
tional data (SDA) pin. The Decoder acts as a slave for receiv-
ing and transmitting data over the serial interface. When the 
serial interface is not active, the logic levels on SCL and 
SDA are pulled HIGH by external pull-up resistors. 
Data received or transmitted on the SDA line must be stable 
for the duration of the positive-going SCL pulse. Data on 
SDA must change only when SCL is LOW. If SDA changes 
state while SCL is HIGH, the serial interface interprets that 
action as a start or stop sequence.
There are six components to serial bus operation:
 Start signal
 Slave address byte
 Block Pointer
 Base register address byte
 Data byte to read or write
 Stop signal 
When the serial interface is inactive (SCL and SDA are 
HIGH) communications are initiated by sending a start sig-
nal. The start signal is a HIGH-to-LOW transition on SDA 
while SCL is HIGH. This signal alerts all slaved devices that 
a data transfer sequence is coming.
The first eight bits of data transferred after a start signal com-
prise a seven bit slave address (the first seven bits) and a sin-
gle R/W bit (the eighth bit). The R/W bit indicates the 
direction of data transfer, read from or write to the slave 
device. If the transmitted slave address matches the address 
of the device (set by the state of the SA
2-0
 input pins in Table 
20), the TMC22x5y acknowledges by bringing SDA LOW 
on the 9th SCL pulse. If the addresses do not match, the 
TMC22x5y does not acknowledge.
Figure 33. Microprocessor Parallel Port – Write Timing
Figure 34. Microprocessor Parallel Port – Read Timing
t
PWLCS
t
SA
t
SD
t
HA
t
HD
t
PWHCS
CS
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R/W
ADR
D
7-0
t
PWLCS
t
SA
t
DOM
t
HA
t
HOM
t
DOZ
t
PWHCS
CS
R/W
ADR
D
7-0
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