Can I compile C-code for the TEMIX (now ATMEL) T89C51RD2 micro using the old "C51 Professional Developers Kit Version 5.1" ? Is it sufficient to use the include file REG51RX2.H available on the website or do I need to upgrade the compiler itself?
Yes. You don't even need the header file to use all the peripherals of any 8051. Just define the sfr's and sbit's in your C files that you use. Here's an example from one of my C files:
// Functional Name Addr Hardware Name sfr r_datBus = 0x80; // P0 sfr r_cmdBus = 0xA0; // P2 (lower 4 bits) sbit r_cmd0 = r_port2 ^ 0; // P2.0 sbit r_cmd1 = r_port2 ^ 1; // P2.1 sbit r_cmd2 = r_port2 ^ 2; // P2.2 sbit r_cmd3 = r_port2 ^ 3; // P2.3 // GAP P2.4 & P2.5 sbit r_req_ = r_port2 ^ 6; // P2.6 sbit r_ack_ = r_port2 ^ 7; // P2.7 sbit r_enableTiIntr = r_ie ^ 0; // IE.EX0 sbit r_TiIntr = r_tcon ^ 1; // TCON.IE0 sbit r_negEdge0 = r_tcon ^ 0; // TCON.IT0