AT76C551 Datasheet, PDF (21/77 Pages) ATMEL Corporation – Single Chip Bluetooth™ Controller

AT76C551
Two 32-bit Timers
Support for
Different
Operating
Frequencies
Table 1. Need Table Caption
Baud Rate
Divisor Used
1200
5000
2400
2500
4800
1250
9600
625
19.2K
312
38.4K
156
57.6K
104
115.2K
52
230.4K
26
460.8K
13
921.6K
6.5
% Error Between Desired and Actual
0
0
0
0
0.16
0.16
0.16
0.16
0.16
0.16
0.16
The UART module provides serial asynchronous receive data synchronization, parallel-to-
serial and serial-to-parallel data conversions for both the transmitter and receiver sections.
These functions are necessary for converting the serial data stream into parallel data which is
required with digital data systems.
Synchronization for the serial data stream is accomplished by adding start and stop bits to the
transmit data to form a data character (character orientated protocol). Data integrity is insured
by attaching a parity bit to the data character for control and monitoring. The parity bit is
checked by the receiver for any transmission bit errors.
AT76C551 includes two identical system timers. Each system timer is a completely indepen-
dent device. Each has adjustable prescale and preload capable of producing interrupts in a
periodic or one-shot fashion.
The AT76C551 chip is able to operate with the following frequencies: 13 MHz, 14.4 MHz, 16.8
MHz and 19.44 MHz. Table 2 shows the correct configuration for each frequency.
Either a crystal or an oscillator can be used. When the OSC_MODE pin is tied to ground the
clock available at the EXT_OSC input is used to drive internal logic. When it is tied to VCC, the
internal clock signal is derived from the XTAL1, XTAL2 pins and associated crystal and
circuitry.
Also a very stable 13 MHz oscillator is required for transceiver operation. This is connected to
the EXT_13_MHZ pin.
Table 2. Correct Configuration Frequencies
CLK_MODE0
0
0
1
1
CLK_MODE1
0
1
0
1
Crystal/Oscillator
Frequency (MHz)
14.4
16.8
19.44
13
21
1612D–08/01