SP2-433-160 Datasheet, PDF (8/27 Pages) Radiometrix Ltd – UHF SpacePort Transceiver

2.2.2 READ A BYTE FROM THE SP2
The sequence for a byte transfer from the SP2 to the HOST (i.e. RX upload) is asynchronous and
proceeds as follows :-
1.
SP2 will assert RX Request line low to initiate transfer
2.
Host pulls RX Accept low (i.e. request is accepted by the host)
3.
SP2 will turn on it's bus drivers, place LS nibble onto data lines
and negate RX Request (set to 1)
4.
Host reads the data and negates RX Accept (i.e. data has been accepted)
Repeat steps 1-4 with MS nibble.
RX-REQUEST
(RXR)
transfer request
data present
RX-ACCEPT
(RXA)
request accept
data has been read
DATA
(4 LINES D0-D3)
LS nibble
Least significant nibble
data may change
MS nibble
most significant nibble
1 byte
figure 7: RX upload timing diagram
Notes:
• The SP2 will turn off it's data bus drivers after the entire packet has been uploaded to the HOST.
• See Appendix B and C. for example SP2 driver subroutines.
2.3 HOST <> SP2 PACKET FORMAT
2.3.1 THE CONTROL BYTE
The first byte of a SP2 <> HOST packet transfer is always the CONTROL BYTE. This byte is used to
control the transfer and contains information about the type of packet, number of bytes to be
transferred, memory address, read/write bit etc. Bit 7 of the control byte is the Packet Type flag, PT, it
determines the class of transfer and the interpretation of the other bits in the control byte.
Radiometrix Ltd, SP2 data sheet
page 8