
EM6517
FOR ENGINEERING ONLY
EM Microelectronic-Marin SA, 09/99, Rev. A/277
29
9
The EM6517-1 has simple Serial Write Buffer which outputs serial data and serial clock.
Serial (Output) Write Buffer - SWB
Serial Write Buffer clock frequency is selected by bits
SWBFSel0
and
SWBFSel1
in
RegSWBCntl
register. The
possible values are 1kHz (default), 2kHz, 8kHz or 16kHz.
The signal TestVar[3], which is used by the processor to make conditional jumps, indicates "Transmission
finished" in automatic send mode or "SWBbuffer empty" in interactive send mode. In interactive mode,
TestVar[3] is equivalent to the interrupt request flags stored in
RegIRQ[i]
registers : it permits to recognize the
interrupt source. (See also the interrupt handling section 13 for further information). To serve the "SWBbuffer
empty " interrupt request, one only has to make a conditional jump on TestVar[3].
The SWB data is output on the rising edge of the clock. Consequently, on the receiver side the serial data can
be evaluated on falling edge of the serial clock edge.
Normally the Clock and the Data output terminals are always driven to ‘0’ outside a SWB data transfer. With a
metal option one can put the Data output, the Clock output or both into a high impedance state outside of a SWB
transfer. Refer to 19.1.4 for the mask settings. The timing going into high impedance state into SWB transfer
and back into high impedance is depending on the selected mode, interactive or automatic.
Figure 22. Serial Write Buffer Architecture
Size[5:0]
Addr. Counter
RAM
SWB buffer
SWBauto
SWBStart
SWBFSel0,1
Control
Logic
Shift register
DB[3:0]
Clk
Mux
SWB clock
SWB data
TestVar3
SWB buffer
register
IRQ (only in
interactive
SWB has two operational modes, automatic mode and interactive mode.
9.1 SWB Automatic send mode
Automatic mode enables a buffer on a predefined length to be sent at high transmission speeds up to ck[15]
(16kHz). In this mode user prepares all the data to be sent (minimum 8 bits, maximum 256 bits) in the RAM.
The user then selects the clock speed, sets the number of data nibbles to be sent, selects automatic
transmission mode (
SWBAuto
bit set to 1) and enters STANDBY mode by executing a HALT instruction. Once
the HALT instruction is activated the SWB peripheral module sends the data in register
RegSWBuff
followed by
the data in the RAM starting at address 00 up to the address specified by the bits
size[5:0]
located in the
RegSWBSizeL, RegSWBSizeH
registers.