Advance Information
National Semiconductor Microwire specifications
provides access to all MT91L60/61 internal read and
write registers. This microport consists of a transmit/
receive data pin (DATA1), a receive data pin
(DATA2), a chip select pin (CS) and a synchronous
data clock pin (SCLK). For D-channel contention
control, in ST-BUS mode, this interface provides an
open-drain interrupt output (IRQ).
The microport dynamically senses the state of the
serial clock (SCLK) each time chip select becomes
active. The device then automatically adjusts its
internal timing and pin configuration to conform to
Intel or Motorola/National requirements. If SCLK is
high during chip select activation then Intel mode 0
timing is assumed. The DATA1 pin is defined as a
bi-directional (transmit/receive) serial port and
DATA2 is internally disconnected. If SCLK is low
during chip select activation then Motorola/National
timing is assumed. Motorola processor mode
CPOL=0, CPHA=0 must be used. DATA1 is defined
as the data transmit pin while DATA2 becomes the
data receive pin. Although the dual port Motorola
controller configuration usually supports full-duplex
communication, only half-duplex communication is
possible in the MT91L60/61. The micro must discard
non-valid data which it clocks in during a valid write
transfer to the MT91L60/61. During a valid read
transfer from the MT91L60/61 data simultaneously
MT91L60/61
clocked out by the micro is ignored by the MT91L60/
61.
All data transfers through the microport are two-byte
transfers requiring the transmission of a Command/
Address byte followed by the data byte written or
read from the addressed register. CS must remain
asserted for the duration of this two-byte transfer. As
shown in Figures 5 and 6 the falling edge of CS
indicates to the MT91L60/61 that a microport
transfer is about to begin. The first 8 clock cycles of
SCLK after the falling edge of CS are always used to
receive the Command/Address byte from the
microcontroller.
The
Command/Address
byte
contains information detailing whether the second
byte transfer will be a read or a write operation and
at what address. The next 8 clock cycles are used to
transfer the data byte between the MT91L60/61 and
the microcontroller. At the end of the two-byte
transfer CS is brought high again to terminate the
session. The rising edge of CS will tri-state the
output driver of DATA1 which will remain tri-stated as
long as CS is high.
Intel processors utilize least significant bit first
transmission while Motorola/National processors
employ most significant bit first transmission. The
MT91L60/61
microport
automatically
accommodates these two schemes for normal data
bytes. However, to ensure decoding of the R/W and
Serial Port
Filter/Codec and Transducer Interface
Default Bypass
-6.0 dB or
0 dB
Receiver
Driver
HSPKR +
75Ω
HSPKR -
75Ω
Handset
Receiver
(150Ω)
PCM
D
in
Decoder
Receive
Filter Gain
0 to -7 dB
(1 dB steps)
-6 dB
Side-tone
-9.96 to
+9. 96 dB
(3.32 dB steps)
-11 dB
PCM
Default Side-tone off
D
out
Encoder
Transmit Filter
Gain
Gain
0 to +7 dB
0
(1 dB steps)
to +7 dB
Transmit Gain
-0.37 dB or 8.93 dB
Transmit
Gain
6.37 dB
M+
M
-
Transmitter
Microphone
Internal To Device
External To Device
Figure 3 - Audio Gain Partitioning
5
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