
Serial Sound Interface
161
Specifications in this manual are tentative and subject to change
Rev. E
MITSUBISHI MICROCOMPUTERS
M30245 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
The data interface for the receiver behaves slightly different for the same case. When the receive shift
register loads data into the left buffer, the state machine generates an interrupt. A word read from the MCU
causes 16 bits to be read. The other 8 bits are latched into a temporary buffer. Latching the data into a
temporary buffer empties the left buffer that provides additional time for the MCU to read the data without an
overflow condition occurring. Even though there are unread bits, no interrupt is generated because a word
read would read a byte from the right buffer which would be invalid data. The data in the right buffer is from
the previous receive cycle and therefore invalid for the read cycle. Thus, the complete read of the left buffer
is delayed until the right buffer is loaded by the receive shift register and the receive interrupts should be
assigned higher priority than transmit if the Serial Sound Interface is set up for both transmit and receive.
The Serial Sound Interface also contains a rate feedback mechanism which can be used to determine the
rate of data transfer via the Serial Sound Interface relative to the USB. It consists of a 16-bit counter with
either SCK or WS as the count source and a 16-bit register to store the count value. The count value is
loaded into the register on each negative edge of SOF pulse generated by the USB core. The counter is
also reset by the SOF pulse. The SOF pulse is a frame delimiter used in USB communication. Refer to the
USB section for details. The value read from the register is the count from the immediately preceding USB
frame.
Figure 1.121 shows the Serial Sound Interface rate feedback registers and Serial Sound Interface transmit
and receive data buffer registers. Figure 1.122. shows the Serial Sound Interface mode registers.
Figure 1.121. Serial Sound Interface related registers (1)
Function
R W
Serial Sound Interface rate feedback register
b7
b8)
(b15
b0
O
X
b7
b0
Symbol
SSIiRF (i = 0, 1)
Address
0319
16, 031816
0379
16, 037816
When reset
0000
16
Rate feedback counter value
Function
R W
Serial Sound Interface transmit buffer register
b7
b8)
(b15
b0 b7
b0
Symbol
SSIiTXB (i = 0, 1)
Address
0315
16, 031416
0375
16, 037416
Transmit data (Note)
X
O
Function
R W
Serial Sound Interface receive buffer register
b7
b8)
(b15
b0 b7
b0
Symbol
SSIiRXB (i = 0, 1)
Address
0317
16, 031616
0377
16, 037616
Receive data (Note)
O
X
Note: Write only to even byte (8 bit) or entire word (16 bit).
Note: Read only from even byte (8 bit) or entire word (16 bit)
When reset
0000
16
When reset
0000
16