AT89C51RC2-3CSCM(2003) 데이터 시트보기 (PDF) - Atmel Corporation
부품명
상세내역
제조사
AT89C51RC2-3CSCM Datasheet PDF : 125 Pages
| |||
Baud Rate
AT89C51RB2/RC2
drive the network. The Master may select each Slave device by software through port
pins (Figure 25). To prevent bus conflicts on the MISO line, only one slave should be
selected at a time by the Master for a transmission.
In a Master configuration, the SS line can be used in conjunction with the MODF flag in
the SPI Status register (SPSTA) to prevent multiple masters from driving MOSI and
SCK (see Error conditions).
A high level on the SS pin puts the MISO line of a Slave SPI in a high-impedance state.
The SS pin could be used as a general-purpose if the following conditions are met:
• The device is configured as a Master and the SSDIS control bit in SPCON is set.
This kind of configuration can be found when only one Master is driving the network
and there is no way that the SS pin could be pulled low. Therefore, the MODF flag in
the SPSTA will never be set(1).
• The Device is configured as a Slave with CPHA and SSDIS control bits set(2). This
kind of configuration can happen when the system comprises one Master and one
Slave only. Therefore, the device should always be selected and there is no reason
that the Master uses the SS pin to select the communicating Slave device.
Note: 1. Clearing SSDIS control bit does not clear MODF.
2. Special care should be taken not to set SSDIS control bit when CPHA = ’0’ because
in this mode, the SS is used to start the transmission.
In Master mode, the baud rate can be selected from a baud rate generator which is con-
trolled by three bits in the SPCON register: SPR2, SPR1 and SPR0.The Master clock is
selected from one of seven clock rates resulting from the division of the internal clock by
2, 4, 8, 16, 32, 64 or 128.
Table 54 gives the different clock rates selected by SPR2:SPR1:SPR0.
Table 54. SPI Master Baud Rate Selection
SPR2
0
0
0
0
1
1
1
1
SPR1
0
0
1
1
0
0
1
1
SPR0
0
1
0
1
0
1
0
1
Clock Rate
Don’t Use
FCLK PERIPH /4
FCLK PERIPH/8
FCLK PERIPH /16
FCLK PERIPH /32
FCLK PERIPH /64
FCLK PERIPH /128
Don’t Use
Baud Rate Divisor (BD)
No BRG
4
8
16
32
64
128
No BRG
67
4180B–8051–04/03
Share Link: 