SAB
SAB
SAF
SAF
5.4 Data Encoding
82525
82526
82525
82526
In the point-to-point configuration, the HSCX supports both NRZ and NRZI data encoding
(selectable via CCR1 register).
NRZ Encoding
1
0
1
1
0
0
1
NRZI Encoding
1
0
1
1
0
0
1
ITT00243
Figure 30
NRZ Encoding/NRZI Encoding
During NRZI encoding, level changes are interpreted as log 0, and no changes in level as
log 1. Since no more than 5 successive log 1’s can appear in a HDLC frame, this type of en-
coding is especially suitable in clock modes, where the clock is recovered from the received
data by means of the DPLL circuits, because at least one transition appears within 5 clock cy-
cles.
Thus, NRZI coding is especially recommended in clock modes 2, 3, 6, 7.
Data output is performed with the rising, data input with the falling clock edge.
5.5 Modem Control Functions (RTS/CTS, CD)
RTS/CTS Handshaking
The HSCX provides two pins (RTS, CTS) per serial channel supporting the standard RTS-CTS
modem handshaking procedure to control the HDLC transmitters.
Data output is performed with the rising clock edge, data input with the falling clock edge. A
transmit request will be indicated by outputting log 0 at the request-to-send output (RTSA/
RTSB). It is also possible to program the RTS outputs by software. After having received the
permission to transmit (CTSA/CTSB) the HSCX transmits a frame.
In the case where permission to transmit is withdrawn during the transmission process, the
frame is aborted (idle). After a new permission to transmit has been received and if all of the
data are still available in the HSCX, the terminated frame will be re-transmitted (self-recovery),
without interrupting the CPU. However, if the permission to transmit is withdrawn after the 32nd
byte in the information field, the transmitter and the XFIFO are reset, the RTS output is deac-
tivated and an interrupt is generated for the
µC.
Semiconductor Group
63
SIEMENS [ Siemens Semiconductor Group ]
