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SA-1110 Developer’s Manual 283
Peripheral Control Module
11.8.5 UDC OUT Maximum Packet Register (UDCOMP)
UDCOMP holds the value of the “maximum packet size minus one” that the SA-1110 UDC will
accept from the Host (Bulk OUT). “Maximum packet size minus one” is used to accommodate a
maximum Data Packet of 256 bytes, without needing a maximum packet size field of more than
8-bits. To allow the SA-1110 UDC to accept a 256-byte (or less) Data Packet from the Host, a value
of 0xff (255) should be written to UDCOMP. After reset of the SA-1110 UDC, UDCOMP contains
0x08, allowing the SA-1110 UDC to accept a 9-byte (or less) Data Packet from the Host. The
SA-1110 UDC will not accept a 0-byte Data Packet into Endpoint 1.
Note: For best performance, Maximum Packet sizes greater than 12-bytes should be limited to Modulo 4
values only, for example, 16-bytes, 64-bytes, 256-bytes.
Note: Due to the internal synchronization required by the SA-1110 UDC configuration registers, it is
possible for the CPU to write to the SA-1110 UDC registers and FIFOs too fast. So, a single write
to the SA-1110 UDC must be completed before another write may take place. To ensure that a
single write is completed, it is necessary to observe the effect of the write before another write may
take place. This can be accomplished by writing to a SA-1110 UDC register and then reading back
the same register two times. The second read-back should produce correct data.
0h 8000 0004 UDCAR Read/Write
7 6 5 4 3 2 1 0
Reserved 7-bit Function Address
Reset
0 0 0 0 0 0 0 0
Bits Name Description
6..0 Address
Function address field
7-bit function address. Reset to zero.
7 —
Reserved.
Always read zero.
0h 8000 0008 UDCOMP Read/Write
7 6 5 4 3 2 1 0
Maximum Packet Size - 1
Reset
0 0 0 0 1 0 0 0
Bits Name Description
7..0 OUT MaxP
OUT maximum packet size.
8-bit field containing the value of the maximum packet size minus one.