Hi,
Well, my comp finally died so I got a new system. Unfortunately, like most modern computers, it has plenty of USB's but doesn't have its parallel port connector installed (but thankfully one RS232). So, no big deal eh? I bought a cheap PCI parallel port card from NETMOS (USB -> lpt cables are useless for download cables). Installed fine, works just like my old comps on-board parallel port cept....
My lattice-isp JTAG cable I built a few years ago no longer works correctly. I've tested the cable on several boards, with several CPLD's. I even built another one to double check. Here is the schem: **broken link removed**
I have checked everything I can think of and so narrowed it down to the parallel port. Now, it DOES correctly program my chips, but only if the chip and programmer are powered by 3.3v. At 5v it just reads crap from the chip and gives an error...which is weird because the chip is a 5v part (min VDD is 4.5v). I can program my chips at 5v if I simply connect the parllel port lines to the CPLD chip via 1k resistors. - without any sort of buffer. The voltage '1' on the new parallel port is a healthy 5.2v via a 3 metre cable.
I can only assume that there is some problems with the voltage levels to and from the parallel port, or possibly noise. This would be the buffer's fault. I've only tried the 74HC244 as well as the VHC. Both have the same trouble. (with unused inputs tied low, decoupling caps etc..).
Can anyone shed some light on this? As I can program these chips 'direct' (no buffer) its no a big problem, but it certainly is annoying and its bugging me.
Blueteeth
Well, my comp finally died so I got a new system. Unfortunately, like most modern computers, it has plenty of USB's but doesn't have its parallel port connector installed (but thankfully one RS232). So, no big deal eh? I bought a cheap PCI parallel port card from NETMOS (USB -> lpt cables are useless for download cables). Installed fine, works just like my old comps on-board parallel port cept....
My lattice-isp JTAG cable I built a few years ago no longer works correctly. I've tested the cable on several boards, with several CPLD's. I even built another one to double check. Here is the schem: **broken link removed**
I have checked everything I can think of and so narrowed it down to the parallel port. Now, it DOES correctly program my chips, but only if the chip and programmer are powered by 3.3v. At 5v it just reads crap from the chip and gives an error...which is weird because the chip is a 5v part (min VDD is 4.5v). I can program my chips at 5v if I simply connect the parllel port lines to the CPLD chip via 1k resistors. - without any sort of buffer. The voltage '1' on the new parallel port is a healthy 5.2v via a 3 metre cable.
I can only assume that there is some problems with the voltage levels to and from the parallel port, or possibly noise. This would be the buffer's fault. I've only tried the 74HC244 as well as the VHC. Both have the same trouble. (with unused inputs tied low, decoupling caps etc..).
Can anyone shed some light on this? As I can program these chips 'direct' (no buffer) its no a big problem, but it certainly is annoying and its bugging me.
Blueteeth