ORCA
Series 3C and 3T FPGAs
Data Sheet
June 1999
Programmable Clock Manager (PCM)
(continued)
PCM Detailed Programming
Descriptions of bit fields and individual control bits in the
PCM
control registers are provided in Table 31. Refer to
Figure 46 for more information on the location of the
PCM
elements that are discussed. In the following discussion,
the duty cycle is in the percentage of the clock period where the clock is high.
Table 31
.
PCM Control Registers
Bit #
Register 0—Divider 0 Programming
4-Bit Divider, DIV0, Value.
This value enables the input clock to immediately be divided by a
value from 1 to 8. A 0 value (the default) indicates that DIV0 is bypassed (no division). Bypass
incurs less delay than dividing by 1. Hexadecimal values greater than 8 for bits [3:0] yield their
modulo 8 value. For example, if bits [3:0] are 1001 (9 hex), the result is divide by 1 (remainder
9/8 = 1).
Reserved.
Bits [6:4]
DIV 0 Reset Bit.
DIV0 may not be reset by GSRN depending on the value of register 7, bit 7.
Bit 7
This bit may be set to 1 to reset DIV0 to its default value. Bit 0 must be set to 0 (the default) to
remove the reset.
Register 1—Divider 1 Programming
4-Bit Divider, DIV1, Value.
This value enables the feedback clock to be divided by a value from
Bits [3:0]
1 to 8. A 0 value (the default) indicates that DIV1 is bypassed (no division). Bypass incurs less
delay than dividing by 1. Hexadecimal values greater than 8 for bits [3:0] yield their modulo 8
value. For example, if bits [3:0] are 1001 (9 hex), the result is divide by 1 (remainder 9/8 = 1).
Reserved.
Bits [6:4]
DIV1 Reset Bit.
DIV1 may not be reset by GSRN, depending on the value of register 7, bit 7.
Bit 7
This bit may be set to 1 to reset DIV1 to its default value. Bit 0 must be set to 0 (the default) to
remove the reset.
Register 2—Divider 2 Programming
4-Bit Divider, DIV2, Value.
This value enables the tapped delay line output clock driven onto
Bits [3:0]
ExpressCLK
to be divided by a value from 1 to 8. A 0 value (the default) indicates that DIV2 is
bypassed (no division). Bypass incurs less delay than dividing by 1. Hexadecimal values greater
than 8 for bits [3:0] yield their modulo 8 value. For example, if bits [3:0] are 1001 (9 hex), the
result is divide by 1 (remainder 9/8 = 1).
Reserved.
Bits [6:4]
DIV2 Reset Bit.
DIV2 may not be reset by GSRN, depending on the value of register 7, bit 7.
Bit 7
This bit may be set to 1 to reset DIV2 to its default value. Bit 7 must be set to 0 (the default) to
remove the reset.
Register 3—DLL 2x Duty-Cycle Programming
Bits [2:0]
Duty-cycle selection for the doubled clock period associated with the input clock high. The duty
cycle is (value of bit 6) * 50% + ((value of bits [2:0]) + 1) * 6.25%. See the description for bit 6.
Bits [5:3]
Duty-cycle selection for the doubled clock period associated with the input clock low. The duty
cycle is (value of bit 7) * 50% + ((value of bits [2:0]) + 1) * 6.25%. See the description for bit 7.
Bit 6
Master duty-cycle control for the first clock period of the doubled clock: 0 = less than or equal to
50%, 1 = greater than 50%.
Bit 7
Master duty-cycle control for the second clock period of the doubled clock: 0 = less than or equal
to 50%, 1 = greater than 50%. Example: Both clock periods having a 62.5% duty cycle, bits [7:0]
are 11 001 001.
Bits [3:0]
Function
80
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