
Universal Serial Bus
85
Specifications in this manual are tentative and subject to change
Rev. E
MITSUBISHI MICROCOMPUTERS
M30245 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
USB ISO Control Register
The USB ISO Control Register, shown in Figure 1.52, contains the isochronous data transfer control and
status information.
ISO_UPD
The ISO_UPD bit is a global bit for endpoints 1-4 and works with IN isochronous pipes only.
When ISO_UPD = “0”, a data packet in an endpoint’s IN buffer is always 'ready to transmit' when it
receives the next IN token from the host (with matched address and endpoint number), if the CPU writes
“1” to the corresponding endpoint’s SET_IN_BUF_RDY bit, or in AUTO_SET case, a data packet equal
to EPx’s MAXP value has been written to the FIFO.
When ISO_UPD = “1” and the ISO bit of the corresponding endpoint’s IN CSR is set, the internal ‘ready
to transmit’ signal to the transmit control logic is not activated when the CPU writes "1" to the correspond-
ing endpoint's SET_IN_BUF_RDY bit, or in the AUTO_SET case, a data packet equal to EPx’s MAXP
value has been written to the FIFO. Instead it is activated when the next SOF is received, thus the data
loaded in frame n is transmitted out in frame n+1.
AUTO_FL
When AUTO_FL = “1”, ISO_UPD = “1”, IN endpoint’s ISO bit is set, and the IN endpoint’s IN_BUF_STS1
& IN_BUF_STS0 are “1”s at the time the USB FCU detects a SOF (from the host or from artificial SOF), it
automatically flushes the oldest packet from the IN buffer. In this case, IN_BUF_STS1 & IN_BUF_STS0
are “1”s and indicate that two data packets are in the IN buffer. Double buffering is required for ISO
transfer.
ART_SOF_ENA
An artificial SOF function enable bit.
ART_SOF_SET
Artificial SOF function status flag. When this flag is “1”, it indicates that an artificial SOF will be generated
by the device because of a missing or corrupt SOF packet (when the SOF enable bit is set to "1"). A
corrupt SOF packet is any SOF having an error in its 8-bit Pakcet ID (PID) field.
CLR_ART_SOF
The CPU writes “1” to this bit to clear the ART_SOF_SET flag.
Figure 1.52. USB ISO Control register (USBISOC)
Bit Symbol
Bit Name
Function
R W
O O
Symbol
USBISOC
Address
028C
16
When reset
0000
16
USB ISO Control register
b7
(b15)
(b8)
b0
b7
b0
0 0000 000
0 : Hardware auto flush disabled
1 : Hardware auto flush enabled
0 : ISO update disabled
1 : ISO update enabled
0 : Artificial SOF disabled
1 : Artificial SOF enabled
0 : Not generated by device (Note 1)
1 : Generated by the device
0 : No action (Note 2)
1 : Clear ART_SOF_SET flag
Must always be set to "0"
O O
AUTO_FL
ISO_UPD
ART_SOF_ENA
ART_SOF_SET
CLR_ART_SOF
Reserved
0
O O
00
Auto flush
ISO Update
Artificial SOF enable
Artificial SOF set flag
Clear artificial SOF set flag
O O
O X
O O
Note 1: Read only
Note 2: Always read "0"