Here's a simple serial driver (simplex.spin) I've been using for some debug stuff. Unlike FullDuplex.spin, it doesn't require its own cog. But be aware: it's output only. Nonetheless, I've made it compatible with FullDuplex so it can be used as a drop-in replacement for those instances where input is not necessary. Also, there's a provision to invert the output for direct connection to an RS232 port.