Attached is a drawing showing possible connection between gps35-hvs and 8051 microcontroller ..
All what you need is a simple inverter; don't use MAX232 as it will not convert signals which are not true RS-232 levels, and gps35-hvs is likely to be such a device ..
I assume you already know that, power to the gps35-hvs is on red (+V=6-40Vdc) and black (0V) ..