NXP Semiconductors LPC24XX UM10237 - Manual (Page 548)

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User manual Rev. 04 — 26 August 2009 548 of 792
NXP Semiconductors
UM10237
Chapter 20: LPC24XX SSP interface SSP0/1
6.4 SSPn Status Register (SSP0SR - 0xE006 800C, SSP1SR -
0xE003 000C)
This read-only register reflects the current status of the SSP controller.
6.5 SSPn Clock Prescale Register (SSP0CPSR - 0xE006 8010, SSP1CPSR
- 0xE003 0010)
This register controls the factor by which the Prescaler divides the SSP peripheral clock
SSP_PCLK to yield the prescaler clock that is, in turn, divided by the SCR factor in
SSPnCR0, to determine the bit clock.
Important: the SSPnCPSR value must be properly initialized or the SSP controller will not
be able to transmit data correctly.
In Slave mode, the SSP clock rate provided by the master must not exceed 1/12 of the
SSP peripheral clock selected in
Section 4–3.3.4 . The content of the SSPnCPSR register
is not relevant.
In master mode, CPSDVSR
min
= 2 or larger (even numbers only).
6.6 SSPn Interrupt Mask Set/Clear Register (SSP0IMSC - 0xE006 8014,
SSP1IMSC - 0xE003 0014)
This register controls whether each of the four possible interrupt conditions in the SSP
controller are enabled. Note that ARM uses the word “masked” in the opposite sense from
classic computer terminology, in which “masked” meant “disabled”. ARM uses the word
“masked” to mean “enabled”. To avoid confusion we will not use the word “masked”.
Table 474: SSPn Status Register (SSP0SR - address 0xE006 800C, SSP1SR - 0xE003 000C)
bit description
Bit Symbol Description Reset Value
0 TFE Transmit FIFO Empty. This bit is 1 is the Transmit FIFO is
empty, 0 if not. 1
1 TNF Transmit FIFO Not Full. This bit is 0 if the Tx FIFO is full, 1 if not. 1
2 RNE Receive FIFO Not Empty. This bit is 0 if the Receive FIFO is
empty, 1 if not. 0
3 RFF Receive FIFO Full. This bit is 1 if the Receive FIFO is full, 0 if
not. 0
4 BSY Busy. This bit is 0 if the SSPn controller is idle, or 1 if it is
currently sending/receiving a frame and/or the Tx FIFO is not
empty. 0
7:5 - Reserved, user software should not write ones to reserved bits.
The value read from a reserved bit is not defined. NA
Table 475: SSPn Clock Prescale Register (SSP0CPSR - address 0xE006 8010, SSP1CPSR -
0xE003 8010) bit description
Bit Symbol Description Reset Value
7:0 CPSDVSR This even value between 2 and 254, by which SSP_PCLK is
divided to yield the prescaler output clock. Bit 0 always reads
as 0.
0