Maxim DS1077 Programmable Oscillator
The Maxim DS1077 is a programmable oscillator. Instead of ordering different oscillators for each different project you have, you get just one on a SparkFun breakout board and program it, using I2C, for whichever frequency you need.
And in fact, after some stumbles on my part, yes, it works.
Things I Learned About the DS1077, The Hard Way
- The I2C interface (a.k.a. TWI or two-wire interface) depends on someone (i.e., you) to pull SCK and SDA high. Toss some pull-up resistors on those lines. I think there’s something cool going on with this protocol that I might be able to exploit for 8821’s bus arbitration. Must read more.
- The Bus Pirate doesn’t turn on its power supply until you tell it to. This is very much a feature, not a bug.
- SDA and SCK are not interchangeable. I hope you didn’t need the internet to tell you that; I almost did.
- The Bus Pirate’s MOSI connection isn’t labeled for I2C, but it’s what drives the SDA line. This makes sense (master-out, slave-in) but I had to look it up to be sure.
- When you’re at your wits’ end and not understanding why your lines are full of random glitches, try changing the wires. Sometimes even simple things like wires can be no good!
For posterity, here’s the Bus Pirate sequence I used to program my DS1077 with an approximately 4.03MHz signal on OUT1, with the two CTRL inputs disabled:
HiZ>m
…
4. I2C
…
(1)>4
I2C mode:
1. Software
2. Hardware
(1)>2
Set speed:
1. 100KHz
2. 400KHz
3. 1MHz
(1)>1
Ready
I2C>W
POWER SUPPLIES ON
I2C>[ 0xb0 0x0d 0b00001000 ] (Don’t write every change to EEPROM)
I2C START BIT
WRITE: 0xB0 ACK
WRITE: 0x0D ACK
WRITE: 0x08 ACK
I2C STOP BIT
I2C>[ 0xb0 002 0b00011000 0b00000000 ] (Use just the 10-bit frequency
divider)
I2C START BIT
WRITE: 0xB0 ACK
WRITE: 0x02 ACK
WRITE: 0x18 ACK
WRITE: 0x00 ACK
I2C STOP BIT
I2C>[0xb0 1 0b00000111 0b11000000] (Write 31 (133MHz/(31+2)) to
divider)
I2C START BIT
WRITE: 0xB0 ACK
WRITE: 0x01 ACK
WRITE: 0x07 ACK
WRITE: 0xC0 ACK
I2C STOP BIT
I2C>[0xb0 0x3f] (Write out the settings to EEPROM)
By the way, this is my first time using the Bus Pirate for a project. I’ve tried a couple times but bounced off because of v4/v3 incompatibility pains. I’m not in love with the interactive serial-terminal interface. But I do appreciate the idiot-proofing, such as starting up with all signals in high- impedance mode. That’ll keep me from destroying my equipment someday, for sure.