參數(shù)資料
型號(hào)： OX16CF950
廠商： Electronic Theatre Controls, Inc.
英文描述： LOW COST ASYNCHRONOUS 16 BIT CARD
中文描述： 低成本異步16位卡
文件頁(yè)數(shù)： 38/60頁(yè)
文件大小： 753K
代理商： OX16CF950
SC
Divisor = DLL + ( 256 x DLM )
Prescaler = 1 when MCR[7] = ‘0’ else:
= M + ( N / 8 ) where:
M
= CPR[7:3] (Integer part – 1 to 31)
N
= CPR[2:0] (Fractional part – 0.000 to 0.875 )
See next section for a discussion of the clock prescaler and
times clock register.
After a hardware reset, the prescaler is bypassed (set to 1)
and TCR is set to 0x00 (.e. SC = 16). Assuming this
default configuration, the following table gives the divisors
required to be programmed into the DLL and DLM registers
in order to obtain various standard baud rates:
DLM:DLL
Divisor Word
0x0900
0x0300
0x0180
0x00C0
0x0060
0x0030
0x0018
0x000C
0x0006
0x0004
0x0003
0x0002
0x0001
Page 38
OXCF950 DATA SHEET V1.1
OXFORD SEMICONDUCTOR LTD.
= Sample clock values defined in TCR[3:0]
Baud Rate
(bits per second)
50
110
300
600
1,200
2,400
4,800
9,600
19,200
28,800
38,400
57,600
115,200
Table 32: Standard PC COM Port Baud Rate Divisors
(assuming a 1.8432MHz crystal)
6.10.2 Clock Prescaler Register ‘CPR’
The CPR register is located at offset 0x01 of the ICR
The prescaler divides the system clock by any value in the
range of 1 to “31 7/8” in steps of 1/8. The divisor takes the
form “M + N/8”, where M is the 5 bit value defined in
CPR[7:3] and N is the 3 bit value defined in CPR[2:0].
The prescaler is by-passed and a prescaler value of ‘1’ is
selected by default when MCR[7] = 0.
MCR[7] is reset to ‘0’ after a hardware reset but may be
overwritten by software. Note however that since access to
MCR[7] is restricted to Enhanced mode only, EFR[4]
should first be set and then MCR[7] set or cleared as
required.
If MCR[7] is set by software, the internal clock prescaler is
enabled.
Upon a hardware reset, CPR defaults to 0x20 (division-by-
4). Compatibility with existing 16C550 baud rate divisors is
maintained using a 1.8432MHz clock.
For higher baud rates use a higher frequency clock, e.g.
14.7456MHz, 18.432MHz, 32MHz, 40MHz or 60.0MHz.
The flexible prescaler allows system designers to generate
popular baud rates using clocks that are not integer
multiples of the required rate. When using a non-standard
clock frequency, compatibility with existing 16C550
software drivers may be maintained with a minor software
patch to program the on-board prescaler to divide the high
frequency clock down to 1.8432MHz.
Table 34 on the following page gives the prescaler values
required to operate the UARTs at compatible baud rates
with various different crystal frequencies. Also given is the
maximum available baud rates in TCR = 16 and TCR = 4
modes with CPR = 1.
6.10.3 Times Clock Register ‘TCR’
The TCR register is located at offset 0x02 of the ICR
The 16C550 and other compatible devices such as 16C650
and 16C750 use a 16 times (16x) over-sampling channel
clock. The 16x over-sampling clock means that the channel
clock runs at 16 times the selected serial bit rate. It limits
the highest baud rate to 1/16 of the system clock when
using a divisor latch value of unity. However, the 950
UART is designed in a manner to enable it to accept other
multiplications of the bit rate clock. It can use values from
4x to 16x clock as programmed in the TCR as long as the
clock (oscillator) frequency error, stability and jitter are
within reasonable parameters. Upon hardware reset the
TCR is reset to 0x00 which means that a 16x clock will be
used, for compatibility with the 16C550 and compatibles.
The maximum baud-rates available for various system
clock frequencies at all of the allowable values of TCR are
indicated in Table 35 on the following page. These are the
values in bits-per-second (bps) that are obtained if the
divisor latch = 0x01 and the Prescaler is set to 1.
The OXCF950 has the facility to operate at baud-rates up
to 15 Mbps at 5V.
The table below indicates how the value in the register
corresponds to the number of clock cycles per bit. TCR[3:0]
is used to program the clock. TCR[7:4] are unused and will
return “0000” if read.
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