M-Bus Data I/O Register (Mdr) - Motorola MC68HC05T16 Technical Data Manual

SRW - Slave R/W Select
1 (set) – Read from slave, from calling master.
0 (clear) – Write to slave from calling master.
When SELTED is set, the R/W command bit of the calling address sent from the master is latched
into this SRW bit. By checking this bit, the CPU can then select slave transmit/receive mode by
configuring XMT bit of the M-Bus Control register.
MIF - M-Bus Interrupt Flag
1 (set) – A M-Bus interrupt has occurred.
0 (clear) – A M-Bus interrupt has not occurred.
When this bit is set, an interrupt is generated to the CPU if MIEN is set. This bit is set when one
of the following events occurs:
1) Completion of one byte of data transfer. It is set at the falling edge of the 9th
clock - MCF set.
2) A match of the calling address with its own specific address in slave receive
mode - SELTED set.
3) A loss of bus arbitration - ALOST set.
This bit must be cleared by software in the interrupt routine.
RXACKB - Receive Acknowledge Bit
1 (set) – No acknowledgment signal detected.
0 (clear) – Acknowledgment signal detected after 8 bits data transmitted.
If cleared, it indicates an acknowledge signal has been received after the completion of 8 bits data
transmission on the bus. If set, no acknowledge signal has been detected at the 9th clock. This is
an active low status flag.
6.3.5

M-Bus Data I/O Register (MDR)

Address bit 7
$3B MD7
In master transmit mode, data written into this register is sent to the bus automatically, with the
most significant bit out first. In master receive mode, reading of this register initiates receiving of
the next byte data. In slave mode, the same function applies after it has been addressed.
MC68HC05T16
bit 6 bit 5 bit 4
MD6 MD5 MD4
M-BUS SERIAL INTERFACE
bit 3 bit 2 bit 1
MD3 MD2 MD1
State
bit 0
on reset
MD0 uuuu uuuu
TPG
MOTOROLA
6-9
6