В юзер гаде на Microblaze напысано:
The block diagram of the MicroBlaze Microcontroller used in this MicroBlaze
Microcontroller Reference Design is shown in Figure 2-1. The design includes an Internal Block RAM memory, an RS232 UART, 4 GPIO blocks, and a JTAG_UART used for software debugging. This configuration utilizes approximately 50% of a Spartan-3™ XC3S200. У меня похожая конфигурация, с большим довеском GPIO не влезла в 200, пришлось ставить 400-й