MT9075B
Preliminary Information
one. Bits 5, 7 and 8 (usually designated X) are spare
bits and are normally set to one if not used.
process. First, writing to the internal Command/
Address Register (CAR) selects one of the 18 pages
of control and status registers (CAR address: AC4 =
0, AC3-AC0 = don't care, CAR data D7 - D0 = page
number). Second, each page has a maximum of 16
registers that are addressed on a read or write to a
non-CAR address (non-CAR: address AC4 = 1, AC3-
AC0 = register address, D7-D0 = data). Once a page
of memory is selected, it is only necessary to write to
the CAR when a different page is to be accessed.
See Figures 11 and 12 for timing requirements.
Time slot 16 of the remaining 15 basic frames of the
CAS multiframe (i.e., basic frames 1 to 15) are
reserved for the ABCD signalling bits for the 30
payload channels. The most significant nibbles are
reserved for channels 1 to 15 and the least
significant nibbles are reserved for channels 16 to
30. That is, time slot 16 of basic frame 1 has ABCD
for channel 1 and 16, time slot 16 of basic frame 2
has ABCD for channel 2 and 17, through to time slot
16 of basic frame 15 has ABCD for channel 15 and
30.
Please note that for microprocessors with read/write
cycles less than 200 ns, a wait state or a dummy
operation (for
C
programming) between two
successive read/write operations to the HDLC FIFO
is required.
MT9075B Access and Control
Register Access
Table 5 associates the MT9075B control and status
pages with access and page descriptions.
The control and status of the MT9075B is achieved
through a non-multiplexed parallel microprocessor
port. The parallel port may be configured for
Motorola style control signals (by setting pin INT/
MOT low) or Intel style control signals (by setting pin
INT/MOT high).
ST-BUS Streams
The ST-BUS stream can also be used to access
channel associated signalling nibbles. CSTo contains
the received channel associated signalling bits (e.g.,
ITU-T R1 and R2 signalling), and when control bit
RPSIG (page 01H, address 1AH) is set to 0, CSTi is
The controlling microprocessor gains access to
specific registers of the MT9075B through a two step
Page Address
Processor
Access
ST-BUS
Access
Register Description
D7 - D0
00000001 (01H)
00000010 (02H)
00000011 (03H)
00000100 (04H)
00000101 (05H)
00000110 (06H)
00000111 (07H)
00001000 (08H)
00001001 (09H)
00001010 (0AH)
00001011 (0BH)
00001100 (0CH)
00001101 (0DH)
00001110 (0EH)
00001111 (0FH)
00010000 (10H)
00010001 (11H)
00010010 (12H)
Master
Control
R/W
R/W
R
--
Master
Status
---
R/W
R/W
R
Per Channel Transmit Signalling
Per Channel Receive Signalling
CSTi
CSTo
Per Time Slot
Control
R/W
R/W
R
---
1 Second Status
---
---
---
---
---
---
---
---
---
---
unused
HDLC0 Control and Status (TS 0)
HDLC1 Control and Status (TS 16)
Transmit National Bit Buffer
Receive National Bit Buffer
Tx message mode Buffer 0
Tx message mode Buffer 1
Rx message mode Buffer 0
Rx message mode Buffer 1
R/W
R/W
R/W
R
R/W
R/W
R/W
R/W
Table 5 - Register Summary
14
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