PURPOSE: To attain the connection of both devices that transfer data at and after the maximum or minimum digit to the same microcomputer, by changing freely the data transfer direction for a serial I/O.
CONSTITUTION: A control register 8 is selected by a decoder 7 which decodes the address signal and delivers signals of high or low levels based on the data of an internal bus 2. These signals decides the shift direction of a shift register 6. Therefore the register 6 is shifted to the right if the register 8 is set by the decoder 7 and the output signal is set at a high level. Then the register 6 is delivered to a transmission terminal Tx from an output buffer 10b through a switch MOSFETQ1 which is turned on and with the MSB (maximum digit bit) set at the head. When the register 8 is reset and the output signal is set at a low level, the register 6 is shifted to the left. Then the data given from the bus 2 is delivered from the side of the LSB (minimum digit bit) through an MOSFETQ2.
OGITA KIYOSHI
YOSHIDA HISAFUMI
HITACHI MICROCUMPUTER ENG