JAJSFZ4E March 2009 – August 2018 TMS320C28341 , TMS320C28342 , TMS320C28343 , TMS320C28344 , TMS320C28345 , TMS320C28346
PRODUCTION DATA.
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The devices have an on-chip, PLL-based clock module. This module provides all the necessary clocking signals for the device, as well as control for low-power mode entry. The PLL has a 5-bit ratio control PLLCR[DIV] to select different CPU clock rates. The watchdog module should be disabled before writing to the PLLCR register. It can be re-enabled (if need be) after the PLL module has stabilized. The input clock and PLLCR[DIV] bits should be chosen in such a way that the output frequency of the PLL (VCOCLK) falls between 400 MHz and 600 MHz. The PLLSTS[DIVSEL] bit should be selected such that SYSCLKOUT(CLKIN) does not exceed the maximum operating frequency allowed for the device (300 MHz or 200 MHz). For example, suppose it is desired to operate a 300-MHz device at 100 MHz using a 20-MHz OSCCLK input (that is, for power savings). The PLL should be configured for OSCCLK * 20, which produces VCOCLK = 400 MHz. PLLSTS[DIVSEL] should then be configured for /4 mode, resulting in the desired 100-MHz CLKIN to the CPU. The PLL should not be configured for OSCCLK * 10 with PLLSTS[DIVSEL] set for /2 mode. This combination would produce VCOCLK = 200 MHz, which does not fall within the required 400 MHz to 600 MHz range.
PLLCR[DIV] VALUE(3)(4) | PLLSTS[DIVSEL] = 0 | PLLSTS[DIVSEL] = 1 | SYSCLKOUT (CLKIN) | |
---|---|---|---|---|
PLLSTS[DIVSEL] = 2 | PLLSTS[DIVSEL] = 3 (2) | |||
00000 (PLL bypass) | OSCCLK/8 (Default) | OSCCLK/4 | OSCCLK/2 | OSCCLK |
00001 | (OSCCLK * 2)/8 | (OSCCLK * 2)/4 | (OSCCLK * 2)/2 | – |
00010 | (OSCCLK * 3)/8 | (OSCCLK * 3)/4 | (OSCCLK * 3)/2 | – |
00011 | (OSCCLK * 4)/8 | (OSCCLK * 4)/4 | (OSCCLK * 4)/2 | – |
00100 | (OSCCLK * 5)/8 | (OSCCLK * 5)/4 | (OSCCLK * 5)/2 | – |
00101 | (OSCCLK * 6)/8 | (OSCCLK * 6)/4 | (OSCCLK * 6)/2 | – |
00110 | (OSCCLK * 7)/8 | (OSCCLK * 7)/4 | (OSCCLK * 7)/2 | – |
00111 | (OSCCLK * 8)/8 | (OSCCLK * 8)/4 | (OSCCLK * 8)/2 | – |
01000 | (OSCCLK * 9)/8 | (OSCCLK * 9)/4 | (OSCCLK * 9)/2 | – |
01001 | (OSCCLK * 10)/8 | (OSCCLK * 10)/4 | (OSCCLK * 10)/2 | – |
01010 | (OSCCLK * 11)/8 | (OSCCLK * 11)/4 | (OSCCLK * 11)/2 | – |
01011 – 11111 | (OSCCLK * 12)/8 –
(OSCCLK * 32)/8 |
(OSCCLK * 12)/4 –
(OSCCLK * 32)/4 |
(OSCCLK * 12)/2 –
(OSCCLK * 32)/2 |
– |
PLLSTS [DIVSEL] | CLKIN DIVIDE |
---|---|
0 | /8 |
1 | /4 |
2 | /2 |
3 | /1 |
The PLL-based clock module provides two modes of operation:
PLL MODE | REMARKS | PLLSTS[DIVSEL](1) | CLKIN AND
SYSCLKOUT |
---|---|---|---|
PLL Off | Invoked by the user setting the PLLOFF bit in the PLLSTS register. The PLL block is disabled in this mode. This can be useful to reduce system noise and for low power operation. The PLLCR register must first be set to 0x0000 (PLL Bypass) before entering this mode. The CPU clock (CLKIN) is derived directly from the input clock on either X1/X2, X1 or XCLKIN. | 0
1 2 3 |
OSCCLK/8
OSCCLK/4 OSCCLK/2 OSCCLK/1 |
PLL Bypass | PLL Bypass is the default PLL configuration upon power up or after an external reset (XRS). This mode is selected when the PLLCR register is set to 0x0000 or while the PLL locks to a new frequency after the PLLCR register has been modified. In this mode, the PLL itself is bypassed but the PLL is not turned off. | 0
1 2 3 |
OSCCLK/8
OSCCLK/4 OSCCLK/2 OSCCLK/1 |
PLL Enable | Achieved by writing a nonzero value n into the PLLCR register. Upon writing to the PLLCR the device will switch to PLL Bypass mode until the PLL locks. | 0
1 2 3 |
OSCCLK*n/8
OSCCLK*n/4 OSCCLK*n/2 –(2) |