PEB2085 SIEMENS [Siemens Semiconductor Group], PEB2085 Datasheet - Page 115

• Manufacturer Part Number: PEB2085
• Description: ISDN SubscribernAccess Controller
• Manufacturer: SIEMENS [Siemens Semiconductor Group]

set), the CPU can write a data block of up to 32 bytes to the transmit FIFO. After this, data
transmission can be initiated by command.
Two different frames types can be transmitted:
– Transparent frame (command: XTF), or
– I frames (command: XIF)
as shown in figure 60.
For transparent frames, the whole frame including address and control field must be written to
the XFIFO.
Figure 60
Transmitter Data Flow
The transmission of I frames is possible only if the ISAC-S is operating in the auto-mode. The
address and control field is autonomously generated by the ISAC-S and appended to the
frame, only the data in the information field must be written to the XFIFO.
If a 2 byte address field has been selected, the ISAC-S takes the contents of the XAD 1 register
to build the high byte of the address field, and the contents of the XAD 2 register to build the
low byte of the address field.
Additionally the C/R bit (bit 1 of the high byte address, as defined by LAPD protocol) is set to
"1" or "0" dependent on whether the frame is a command or a response.
Semiconductor Group
HDLC Frame
Transmit I-Frame
(XIF)
Auto Mode, 8-Bit Addr.
Transmit I-Frame
(XIF)
Auto Mode,
Transmit Transparent
Frame (XTF)
All Modes
-
16-Bit Addr.
Note: Length of Control Field is b or 16
Description of Symbols:
Flag
Flag
Flag
Flag
XAD1
Generated automatically by
Written initially by CPU
Loaded (repeatedly)
request
Address
XAD1
XAD2
(XPR Interrupt)
115
Control
Control
Control
XFIFO
by CPU upon
(Info Register)
Bit
ISAC -S
Information
XFIFO
XFIFO
R
ISAC -S
R
Functional Description
CRC
CRC
CRC
CRC
Flag
Flag
Flag
Flag
ITD02341