Bt8370/8375/8376
2.0 Circuit Description
Fully Integrated T1/E1 Framer and Line Interface
2.10 Microprocessor Interface
2.10.4 Device Reset
The Bt8370/8375/8376 contains three reset methods: internal power-on reset
(POR), hardware reset which uses the RST* pin, and software reset which uses
the RESET bit in register CR0 [addr 001]. All three methods result in device
outputs placed in a high-impedance state and configuration registers set to default
values as shown in Table 3-1, Address Map. In all reset methods, both REFCLK
and MCLK (internal or external) must be present during the reset process for
proper operation. MCLK (internal or external) performs the actual register
initialization. Therefore, if the CLKMD pin is connected high to enable external
MCLK, the external MCLK must be applied during reset, and if the CLKMD pin
is low during reset, the internal clock (33 MHz) is used.
After hardware reset, software reset, or internal power-on reset, the
microprocessor must initialize Bt8370/8375/8376 control registers and buffer
memory registers to the desired state.
2.10.4.1 Power-On
Reset (POR)
An internal POR process is initiated during power-up. When VDD has reached
approximately 3 V, the internal reset process begins and continues for 2048
REFCLK cycles (approximately 205 µs) if REFCLK is applied. If REFCLK is
not present, the Bt8370/8375/8376 remains in the reset state and does not
terminate until detecting 2048 REFCLK cycles have been detected. The RESET
bit in register CR0 [addr 001] can be monitored to determine when POR is
complete. MCLK (internal or external) must be present during the POR
concurrent with REFCLK to allow register initialization.
The LOOP register [addr 014] is not reset during power-on reset or internal
reset so the device may occasionally power-on in a loopback state. If this occurs,
several other registers (e.g., several IER registers) may not properly reset to their
default values. To avoid this, after power-on or hardware reset, write the Loop
register to 0 and then initiate a software reset using the RESET bit in the Primary
Control register [CR0; addr 001]. After this procedure, all default registers have
their default values. XOE needs to be disabled during the power-on reset period
and re-enabled after configuring the part. The device must not be in Framer
Loopback State when the software reset is written.
2.10.4.2 Hardware
Reset
Hardware Reset is initiated by bringing the RST* pin active (low) for a minimum
of 4 µs. If CLKMD is high (using external MCLK), external MCLK must be
present while RST* is low to allow register initialization. After RST* is
deactivated, the internal reset process continues for 5 µs, and register access must
be avoided. The RESET bit in register CR0 [addr 001] can be monitored to
determine when the reset process is complete.
2.10.4.3 Software Reset
Software Reset is initiated by writing the RESET bit [register CR0; addr 001] to
0, delaying at least 6 µs, then writing RESET to 1. Once initiated, the reset
process continues for 15 µs maximum and register access must be avoided. The
RESET bit can be monitored to determine when the reset process has completed.
As with the other reset methods, both REFCLK and MCLK (internal or external)
must be present during the reset process.
N8370DSE
Conexant
2-85
CONEXANT [ CONEXANT SYSTEMS, INC ]
