Pepper Computer Modular Computers RS485 - Manual (Page 304)

SMART I/O User’s Manual
October 01, 1996 ©1996 PEP Modular Computers GmbH Page 6- 22
Chapter 6 Communications Modules
6.2.7 Register Description
The SM-SSI SMART-Module connected to a SMART I/O slot uses the SPI
transparent mode for on-board data reading and writing and 5 parallel lines
for data selection. On board are a set of registers and peripherals shown in
the table below:
Due to the fact that SPI transmissions are full duplex, some read only regis-
ters are accessed at the same time as write only registers in order to optimize
data transmission. Therefore, when the Control Register is written to, simul-
taneously the Status Register is read and similarly when writing to the
Compare Register, the Data Register is read.
256 bytes of serial EEPROM contain the module ID number and production
data although and further space has been allocated for future use.
6.2.7.1 Control Register
The 24-bit control register is divided into three sub-registers which are
cleared after a power-on reset and control:
• FDL: Format Data Length • AR : Automatic Reading Mode
• P : Parity Enable/Disable • RST : Encoder Reset Control
• ENI : Interrupt Masks • PT : Parity Type (Odd/Even)
• SOT: Start Transmission • DT : Data Type (Gray/Binary)
• CF : Data Clock Frequency • CM : Clear Match output
N o . Description Direction
1 Internal 16-bit Status Register Read Only
1 Internal 24-bit Control Register Write Only
1 Internal 8-bit Identification Register Read Only
1 Internal 24-bit Data Register Read Only
1 Internal 24-bit Compare Register Write Only
1 SPI compatible serial EEPROM Read/Write
1 Optional SPI compatible serial Digital to Analog Converter Read/Write