Preliminary
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Registers
Table 9-31. SD System Control Register (SD_SYSCTL) Field Descriptions (continued)
Bit
Field
Value
Description
19-16
DTO
Data timeout counter value and busy timeout. This value determines the interval by which SD_DAT
lines timeouts are detected.
The host driver needs to set this bit field based on:
• The maximum read access time (NAC) (Refer to the SD Specification Part1 Physical Layer)
• The data read access time values (TAAC and NSAC) in the card specific data register (CSD) of
the card
• The timeout clock base frequency (SD_CAPA[5:0] TCF bits)
If the card does not respond within the specified number of cycles, a data timeout error occurs
(SD_STAT[20] DTO bit). The SD_SYSCTL[19,16] DTO bit field is also used to check busy duration,
to generate busy timeout for commands with busy response or for busy programming during a write
command. Timeout on CRC status is generated if no CRC token is present after a block write.
0
TCF x 2^13
1h
TCF x 2^14
Eh
TCF x 2^27
Fh
Reserved
15-6
CLKD
Clock frequency select. These bits define the ratio between a reference clock frequency (system
dependant) and the output clock frequency on the SD_CLK pin of either the memory card (SD or
SDIO).
0
Clock Ref bypass
1h
Clock Ref bypass
2h
Clock Ref / 2
3h
Clock Ref / 3
3FFh
Clock Ref / 1023
5-3
Reserved
0
Reserved bit field. Do not write any value.
2
CEN
Clock enable. This bit controls if the clock is provided to the card or not.
0
The clock is not provided to the card . Clock frequency can be changed .
1
The clock is provided to the card and can be automatically gated when SD_SYSCONFIG[0]
AUTOIDLE bit is set to 1 (default value) .
The host driver shall wait to set this bit to 1 until the Internal clock is stable (SD_SYSCTL[1] ICS
bit).
1
ICS
Internal clock stable (status)This bit indicates either the internal clock is stable or not.
0
The internal clock is not stable.
1
The internal clock is stable after enabling the clock (SD_SYSCTL[0] ICE bit) or after changing the
clock ratio (SD_SYSCTL[15:6] CLKD bits).
0
ICE
Internal clock enable. This register controls the internal clock activity. In very low power state, the
internal clock is stopped. NoteThe activity of the debounce clock (used for wake-up events) and the
interface clock (used for reads and writes to the module register map) are not affected by this
register.
0
The internal clock is stopped (very low power state).
1
The internal clock oscillates and can be automatically gated when SD_SYSCONFIG[0] AUTOIDLE
bit is set to 1 (default value).
989
SPRUGX9 – 15 April 2011
Secure Digital (SD)/—Secure Digital I/O (SDIO) Card Interface
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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