Datasheet

ST7538Q Functional description
19/44
The UART interface allows to connect an UART compatible device instead SPI interface
allows to connect an SPI compatible device. The allowed combinations of Host
Interface/ST7538Q Mains Access are:
Figure 3. Synchronous and asynchronous ST7538Q/Host controller interfaces
ST7538Q allows to interface the Host Controller using a five line interface (RxD,TxD,RxTx,
CLR/T, & REG_DATA) in case of Synchronous mains access or using a 3 line interface
(RxD,TxD & RxTx) in Asynchronous mains access. Since Control Register is not accessible
in Asynchronous mode, in this case REG_DATA pin can be tied to GND.
Table 9. Host Interface / ST7538Q mains access combinations
Host Device
interface type
UART/SPI pin
Communication
mode
Mains access
Asynchronous Synchronous
UART “1” Transmission X
UART “1” Reception X
X
(1)
1. Received Data more stable than in Asynchronous Mains Access
SPI “0” Transmission X
SPI “0” Reception X
RxD
CLR/T
REG_DATA
RxTx
ST7538QHost Controller
TxD
UART/Asynchronous
Data Interface
RxD
CLR/T
REG_DATA
RxTx
ST7538QHost Controller
TxD
SPI/Synchronous
Data Interface
D03IN1415