C541U_99 Datasheet, PDF (125/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
Bit
LEN3 - 0
Function
Length Information
contains the number of bytes currently stored in the USB data registers. LEN is
set to 1111_B when the hardware accesing the USBDRn registers. Bitfield LEN is
updated either by USB or by CPU.
CPU: The number of bytes (packet size) has to be written to bitfield LEN at the
end of a CPU write access to the USB data registers. Note that setting TYPE to
EMPTY after a CPU read access, will causes bitfield LEN to be reset.
USB: The number of received bytes (the size of the received packet) is written to
bitfield LEN after an USB write accesss, while LEN is reset after the data packet
was read by the USB.
Move immediate data to USBDCR registers are unsupported. An example of such instructions is as
the following :
MOV
USBDCR,#12H
;The data 12H is just an example and can be replaced
; with any 8-bit immediate data.
It is recommended to use a temporary register or an accumulator to write to these registers.
Examples of using accumulator and register are as the following :
MOV
MOV
A,#12H
USBDCR,A
;Move immediate data to accumulator
;Move the content of accumulator into USBDCR register
MOV
MOV
R2,#12H
USBDCR,R2
;Move immediate data to R2
;Move the content of R2 into USBDCR register
Semiconductor Group
6-80
1999-04-01